本文围绕工程valgrind-sample进行讲解。 先看下工程结构：
methods类写了几个可能存在内存操作问题的函数， main.cpp调用methods类函数：
methods.h:
<code class="hljs vala has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifndef VALGRIND_METHODS_H </span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#define VALGRIND_METHODS_H </span><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">namespace</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">sample</span>{</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> printx(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> access_violation();<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> mem_overlap(); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> nonfree();
}
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif //VALGRIND_METHODS_H</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul> main.cpp:
<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-id" style="box-sizing: border-box; color: rgb(155, 112, 63);">#include</span> <<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">iostream</span>>
<span class="hljs-id" style="box-sizing: border-box; color: rgb(155, 112, 63);">#include</span> "<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">methods</span><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.h</span>"
<span class="hljs-id" style="box-sizing: border-box; color: rgb(155, 112, 63);">#include</span> <<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">string</span><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.h</span>> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">int</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">main</span>(<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">int</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">argc</span>, <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">char</span> *<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">argv</span><span class="hljs-attr_selector" style="color: rgb(0, 136, 0); box-sizing: border-box;">[]</span>)<span class="hljs-rules" style="box-sizing: border-box;">{ <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">sample</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);">:<span class="hljs-function" style="box-sizing: border-box;">printx()</span></span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">sample</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);">:<span class="hljs-function" style="box-sizing: border-box;">access_violation()</span></span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">sample</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);">:<span class="hljs-function" style="box-sizing: border-box;">mem_overlap()</span></span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">sample</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);">:<span class="hljs-function" style="box-sizing: border-box;">nonfree()</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span> </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>
下面分别看这几个函数可能会遇到什么问题。
1. sample::printx()
<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> printx(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (x == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"X is zero"</span>); }
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul> 问题显而易见， 变量赋值前引用， 但C编译器并不会报错。
valgrind ./valgrind-sample:
==17495== Conditional jump or move depends on uninitialised value(s)
==17495== at 0x400D10: sample::printx() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==17495== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
2. sample::access_violation()
<code class="hljs perl has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">void access_violation(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> len = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*pt</span> = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*)</span>malloc(len<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*sizeof</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>)); <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//problem</span>1: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">not</span> freed<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*p</span> = pt; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < len; i++){ p++; } <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*p</span> = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//problem</span>2: heap block overrun <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">%d</span>\n"</span>, <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">*p</span>); <span class="hljs-regexp" style="color: rgb(0, 136, 0); box-sizing: border-box;">//problem</span>3: heap block overrun
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul> 问题如code所示，
line3: 指针pt申请了空间，但是没有释放;
line8: pt申请了5个int的空间，p经过4次循环（i=3时）已达到最后申请的p[4], 在i=4时p所指向的空间没有申请过; (下面valgrind报告中 Invalid write of size 4)
line9: 同line8 (下面valgrind报告中 Invalid read of size 4 )
valgrind ./valgrind-sample:
==21058== Invalid write of size 4
==21058== at 0x400D74: sample::access_violation() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== Address 0x4b32054 is 0 bytes after a block of size 20 alloc’d
==21058== at 0x490514E: malloc (vg_replace_malloc.c:195)
==21058== by 0x400D44: sample::access_violation() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058==
==21058== Invalid read of size 4
==21058== at 0x400D7E: sample::access_violation() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== Address 0x4b32054 is 0 bytes after a block of size 20 alloc’d
==21058== at 0x490514E: malloc (vg_replace_malloc.c:195)
==21058== by 0x400D44: sample::access_violation() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==21058==
3. sample::mem_overlap()
<code class="hljs axapta has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> mem_overlap(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>]; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>; i++){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>[i] = i; } memcpy(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span> + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> x[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"abcd"</span>; strncpy(x + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>, x, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>);
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul> 问题出在memcpy上， 将str指针位置开始copy 5个char到str+1所指空间，会造成内存覆盖。strncpy也是同理。
valgrind ./valgrind-sample:
==27473== Source and destination overlap in memcpy(0x7feffedc1, 0x7feffedc0, 5)
==27473== at 0x4907566: memcpy (mc_replace_strmem.c:482)
==27473== by 0x400DD1: sample::mem_overlap() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==27473== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==27473==
==27473== Source and destination overlap in strncpy(0x7feffeda5, 0x7feffeda3, 3)
==27473== at 0x490737B: strncpy (mc_replace_strmem.c:329)
==27473== by 0x400DFA: sample::mem_overlap() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==27473== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
4. sample::nonfree()
<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> nonfree(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* str = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>*)<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">malloc</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>*<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>)); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* ptr = str; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">delete</span> [] ptr; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<mismatch>: delete - new; malloc - free</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">free</span>(str); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<invalid>: release freed memory </span>ptr[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'a'</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<invalid>: use released memory </span>
} </code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul> 问题如code所示。
line 4: 用malloc申请空间的指针用free释放；用new申请的空间用delete释放 (valgrind中Mismatched free() / delete / delete [])；
line 5: 由于ptr=str, ptr已被释放，str无需再释放，此处释放了已经被释放的内存（valgrind中 Invalid free() / delete / delete[]）；
line 6: 用到了已经被释放的内存（valgrind中Invalid write of size 1）；
valgrind ./valgrind-sample:
==29210== Mismatched free() / delete / delete []
==29210== at 0x4906510: operator delete (vg_replace_malloc.c:368)
==29210== by 0x400E2B: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== Address 0x4b32040 is 0 bytes inside a block of size 5 alloc’d
==29210== at 0x490514E: malloc (vg_replace_malloc.c:195)
==29210== by 0x400E0F: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210==
==29210== Invalid free() / delete / delete[]
==29210== at 0x4905E72: free (vg_replace_malloc.c:325)
==29210== by 0x400E34: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== Address 0x4b32040 is 0 bytes inside a block of size 5 free’d
==29210== at 0x4906510: operator delete (vg_replace_malloc.c:368)
==29210== by 0x400E2B: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210==
==29210== Invalid write of size 1
==29210== at 0x400E3C: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== Address 0x4b32041 is 1 bytes inside a block of size 5 free’d
==29210== at 0x4906510: operator delete (vg_replace_malloc.c:368)
==29210== by 0x400E2B: sample::nonfree() (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
==29210== by 0x400B4B: main (in /home/zhangruiqing01/disk2/study/code/valgrind-samples/valgrind-samples)
最后，整个methods.cpp文件如下：
methods.cpp:
<code class="hljs cpp has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <iostream> </span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <stdio.h> </span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include <string.h> </span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#include "methods.h" </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">namespace</span> sample{ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> printx(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> x; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (x == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>) { <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"X is zero"</span>); } } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> access_violation(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> len = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *pt = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>*)<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">malloc</span>(len*<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span>)); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem1: not freed </span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> *p = pt; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < len; i++){ p++; } *p = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem2: heap block overrun </span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">printf</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%d\n"</span>, *p); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem3: heap block overrun </span>} <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> mem_overlap(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> str[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>]; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> i = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>; i < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>; i++){ str[i] = i; } <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">memcpy</span>(str + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>, str, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> x[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"abcd"</span>; <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">strncpy</span>(x + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>, x, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>); } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> nonfree(){ <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* str = (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>*)<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">malloc</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span>*<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">sizeof</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>)); <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span>* ptr = str; <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">delete</span> [] ptr; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<mismatch>: delete - new; malloc - free </span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">free</span>(str); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<invalid>: release freed memory </span>ptr[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'a'</span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//problem<invalid>: use released memory </span>}
} </code>
