c++ string构造函数和assign函数

c++ string构造函数和assign函数

#include <iostream>
#include <stdlib.h>
#include <string>
#include <string.h>int main()
{char buff[10] = {'a','b','c','d','e','f','g','h','i','\0'};std::string str1;str1.assign(&buff[0],0,10);int length = str1.length();int len    = strlen(str1.c_str());std::cout<<"test1: length="<<length<<",len="<<len<<std::endl;std::string str2 = std::string((char*)&buff[0],10);length = str2.length();len    = strlen(str2.c_str());std::cout<<"test2: length="<<length<<",len="<<len<<std::endl;std::string str3 = str2;length = str3.length();len    = strlen(str3.c_str());std::cout<<"test3: length="<<length<<",len="<<len<<std::endl;std::string str4;str4.assign(str3.c_str(),strlen(str3.c_str()));length = str4.length();len    = strlen(str4.c_str());std::cout<<"test4: length="<<length<<",len="<<len<<std::endl;return 0;	
}

[banting@localhost test]$ vim test.cpp
[banting@localhost test]$ g++ -g test.cpp -o test
[banting@localhost test]$ ./test
test1: length=9,len=9
test2: length=10,len=9
test3: length=10,len=9
test4: length=9,len=9
[banting@localhost test]$ 

结论：

为什么上述构造函数和assign函数，不同赋值,通过C++ string的成员函函数length()得到结果不一样？
因为不同函数操作，对length长度计算方式不一样 ，兼容C的接口，字符串结束符’\0’不计入长度。

参考文献

https://cplusplus.com/reference/string/string/string/
https://cplusplus.com/reference/string/string/assign/