C字符串到C和C ++中的大写 [英] C string to uppercase in C and C++

问题描述

当我在C ++中组合一个大写字母函数时，我注意到我没有收到C中的预期输出。

While I was putting together a to-uppercase function in C++ I noticed that I did not receive the expected output in C.

C ++函数

C++ function

#include <iostream>
#include <cctype>
#include <cstdio>

void strupp(char* beg)
{
    while (*beg++ = std::toupper(*beg));
}

int main(int charc, char* argv[])
{
    char a[] = "foobar";
    strupp(a);
    printf("%s\n", a);
    return 0;
}

按预期输出：

FOOBAR

---

C函数

#include <ctype.h>
#include <stdio.h>
#include <string.h>

void strupp(char* beg)
{
    while (*beg++ = toupper(*beg));
}

int main(int charc, char* argv[])
{
    char a[] = "foobar";
    strupp(a);
    printf("%s\n", a);
    return 0;
}

输出是缺少第一个字符的预期结果

The output is the expected result with the first character missing

OOBAR

任何人都知道为什么结果在C？中编译时被截断。

Does anyone know why the result gets truncated while compiling in C?

推荐答案

问题是

while (*beg++ = toupper(*beg));

所以我们有未定义的行为。编译器在这种情况下做的是评估 beg ++ 之前 toupper（* beg）在C中，换一种方式。

So we have undefined behavior. What the compiler is doing in this case is evaluating beg++ before toupper(*beg) In C where in C++ it is doing it the other way.

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