让Visual Studio的警告未签名的比较 [英] Make Visual Studio warn for unsigned comparisons

问题描述

这code，当使用Visual Studio 2010编译

This code, when compiled with Visual Studio 2010

#include <cstdlib>
#include <cstdio>

int numbers[] = { 23, 24, 25, 25, 28, 20, 20 };

int main(void) {
    int d = -1, x=0;
    size_t count = sizeof(numbers) / sizeof(numbers[0]);

    if (d <= (sizeof(numbers) / sizeof(numbers[0]))-2)
        x = numbers[d+1];

    if (d <= count-2)
        x = numbers[d+1];
}

给我一个符号/无符号不匹配的警告如果（D＆LT; =计数2）而不是在如果（D＆LT; = （sizeof的（数字）/ sizeof的（编号[0]）） - 2）。为什么是这样？我已经启用的所有的警告。

gives me a signed/unsigned mismatch warning on if (d <= count-2) but not on if (d <= (sizeof(numbers) / sizeof(numbers[0]))-2). Why is this? I have enabled all warnings.

推荐答案

这是在Visual C ++编译器不会发出在这种情况下警告C4018的错误。请参阅Microsoft连接错误报告，<一个href=\"http://connect.microsoft.com/VisualStudio/feedback/details/569898/warning-c4018-signed-unsigned-mismatch-for-sizeof-operator\"相对=nofollow>警告C4018（符号/无符号不匹配）的sizeof操作符。

It is a bug that the Visual C++ compiler does not emit warning C4018 in this case. See the Microsoft Connect bug report, "warning C4018 (signed/unsigned mismatch) for sizeof operator."

这个问题似乎只有间接关系的的使用的sizeof 。编译器还没有发出在其他情况下，警告，其中无符号类型的一个恒定值是参与了比较。例如，如果您添加常量企业资质为计数，C4018甚至没有你的第二个比较发射。

The issue appears to be only indirectly related to usage of sizeof. The compiler also fails to emit the warning in other cases where a constant value of unsigned type is involved in the comparison. For example, if you add const-qualification to count, C4018 is not emitted even for your second comparison.

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