对char *进行相等测试std :: string，operator ==()始终安全吗? [英] Equality-test std::string against char*, is operator==() always safe?

问题描述

std :: string 的STL运算符和重载是否意味着使用 operator == 比较 char * 是安全的针对 std :: string ，不受限制，这是LHS/RHS?

Do the STL operators and overloads for std::string mean that it is safe to use operator== to compare a char* against a std::string, without restriction which is the LHS/RHS?

推荐答案

不，不受限制是不安全的.限制为:

No, it is not safe without restrictions. The restrictions are:

• char * 不能为空指针.
• char * 指向的字符序列必须以零定界(即以 \ 0 结尾)

• the char* must not be a nullpointer.
• the character sequence pointed to by the char* has to be zero-delimited (i.e. end with a \0)

但是，哪一个放在左边和哪一个放在右边并不重要-它给出相同的结果.

But it is not important which one you put left and which one right - it gives the same result.

但是有一个警告: std :: string s可能包含 \ 0 个不在结尾的字符.将其中一个与 char * 字符序列进行比较将始终为false，因为比较将在 char * \ 0 处停止>.

But there's a caveat: std::strings may contain \0 characters that are not at the end. Comparing one of those against a char* character sequence will always give false, because the comparison will stop at the first \0 encountered in the char*.

示例:

char c[] = "Hello\0 World!";
std::string s(c, sizeof(c));

std::cout << ((s == c) ? "ok" : "meh") << '\n';  //meh    - compares only until the first \0
std::cout << c << '\n';                          //Hello  - cout also stops at first \0
std::cout << s << '\n';                          //Hello World!

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