如何在编译时静态比较两个字符串 [英] How can you compare two character strings statically at compile time

问题描述

我想创建一个宏，它可以比较2个字符串，并发出编译时错误，如果条件不满足。这可能是一个编译时断言。

I would like to create a macro which can compare 2 strings, and emit a compile time error if the condition isn't met. This could be though of as a compile time assertion.

我不知道我该怎么做。

例如：

STATIC_COMPARE("THIS STRING","THIS STRING") -> would emit a compile time error
STATIC_COMPARE("THIS STRING","THIS OTHER STRING) -> wouldn't emit a compile time error.

宏将类似于

#define STATIC_COMPARE(str1,str2) if (str1==str2) emit an error with a message

所以我想问题归化在编译时可以比较2个字符串。

So I guess the question boils down to being able to compare the 2 strings at compile time.

推荐答案

可以使用C ++ 11通过使用 constexpr function：

You can do this with C++11 by using a constexpr function:

constexpr bool strings_equal(char const * a, char const * b) {
    return *a == *b && (*a == '\0' || strings_equal(a + 1, b + 1));
}

（请参阅一个演示）

在C ++ 11之前不可能做到这一点，许多编译器将编译等号字符串作为指针的警告在这些编译器上，直接比较字符串就足够了，因为它们都将被作为等指针来计算。

It's not possible to do this prior to C++11, with the caveat that many compilers will compile equal string literals to be a pointer to the same location. On these compilers it's sufficient to compare the strings directly since they will both be evaluated as equal pointers.

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