可优先使用std::string_view作为函数入参

本文主要是介绍可优先使用std::string_view作为函数入参，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

如下的代码，当只提供入参是std::string的版本时，当传入const char*时会构造一个std::string对象。

#include <iostream>
#include <format>
#include <string>
#include <string_view>
#include <iomanip>void print(const std::string& str){std::cout << "**version1**, " << __func__ << ", " << str << std::endl;
}/*void print(const char* str){std::cout << "--version2--, " << __func__ << ", " << str << std::endl;
}void print(const std::string_view str){std::cout << "==version3==, " << __func__ << ", " << str << std::endl;
}*/auto main()->int{const char* ch = "const char*";std::string str("std::string");print(ch);   // **version1**, print, const char*print(str);  // **version1**, print, std::string
}

可以提供重载的print来避免上述问题，不过会增加代码量。

#include <iostream>
#include <format>
#include <string>
#include <string_view>
#include <iomanip>void print(const std::string& str){std::cout << "**version1**, " << __func__ << ", " << str << std::endl;
}void print(const char* str){std::cout << "--version2--, " << __func__ << ", " << str << std::endl;
}/*void print(const std::string_view str){std::cout << "==version3==, " << __func__ << ", " << str << std::endl;
}*/auto main()->int{const char* ch = "const char*";std::string str("std::string");print(ch);   // --version2--, print, const char*print(str);  // **version1**, print, std::string
}

而使用std::string_view作为入参可以同时兼容入参是std::string和const char*的情况。

#include <iostream>
#include <format>
#include <string>
#include <string_view>
#include <iomanip>/*void print(const std::string& str){std::cout << "**version1**, " << __func__ << ", " << str << std::endl;
}void print(const char* str){std::cout << "--version2--, " << __func__ << ", " << str << std::endl;
}*/void print(const std::string_view str){std::cout << "==version3==, " << __func__ << ", " << str << std::endl;
}auto main()->int{const char* ch = "const char*";std::string str("std::string");print(ch);   // ==version3==, print, const char*print(str);  // ==version3==, print, std::string
}

但是当三个版本的print都提供时编译器还是会进行最佳匹配。

#include <iostream>
#include <format>
#include <string>
#include <string_view>
#include <iomanip>void print(const std::string& str){std::cout << "**version1**, " << __func__ << ", " << str << std::endl;
}void print(const char* str){std::cout << "--version2--, " << __func__ << ", " << str << std::endl;
}void print(const std::string_view str){std::cout << "==version3==, " << __func__ << ", " << str << std::endl;
}auto main()->int{const char* ch = "const char*";std::string str("std::string");print(ch);   // --version2--, print, const char*print(str);  // **version1**, print, std::string
}