如何获取 if 语句中赋值的编译器错误？

Question

在 Visual Studio 中是否有可能因语句中的赋值而出现编译器错误if？如何？

#include <iostream>
int main()
{
    int a = 2;
    if (a = 3)  // Want a warning here
        std::cout << "Avoid this!\n";
}

我知道我可以切换到尤达条件 ( if (3=a))，但我真的不想这样做。

我尝试过：将警告级别设置为/Wall，但我仍然没有收到可以将其视为错误的警告。

我正在 Visual Studio 2019 (16.11.19) 中执行此操作：

构建输出是

Rebuild started...
1>------ Rebuild All started: Project: Yoda2019, Configuration: Debug Win32 ------
1>Yoda2019.cpp
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\limits.h(70,5): error C2220: the following warning is treated as an error
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\limits.h(70,5): warning C4668: '__STDC_WANT_SECURE_LIB__' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xmemory(154,5): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\xmemory(164,5): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\atomic(284,9): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\atomic(299,9): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\atomic(315,9): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.29.30133\include\atomic(375,9): warning C4365: 'argument': conversion from 'long' to 'unsigned int', signed/unsigned mismatch
1>Done building project "Yoda2019.vcxproj" -- FAILED.
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

和 Visual Studio 2022 (17.4.0)

构建输出是

Rebuild started...
1>------ Rebuild All started: Project: YodaCheck, Configuration: Debug x64 ------
1>YodaCheck.cpp
1>YodaCheck.vcxproj -> B:\Projekte\C++\Dynamic Linking\YodaCheck\x64\Debug\YodaCheck.exe
========== Rebuild All: 1 succeeded, 0 failed, 0 skipped ==========
========== Elapsed 00:01,379 ==========

所以我没有看到可以转换为错误的警告。

Answer 1

使用/W4 /WX

/WX将所有编译器警告视为错误。对于一个新项目，最好在所有编译中使用/WX；解决所有警告可确保尽可能减少难以发现的代码缺陷。

https://learn.microsoft.com/en-us/cpp/build/reference/compiler-option-warning-level?view=msvc-170

确保在相关配置中进行该设置。在这样一个简单的演示中，选择“所有配置”和“所有平台”可能是最简单的。

Answer 2

您可以使用该指令将任何特定警告转变为错误#pragma warning(error:nnnn)。在您的情况下，警告是：

警告 C4706：条件表达式内的赋值

#pragma因此，在代码中添加相关指令将产生编译器错误：

#include <iostream>
#pragma warning(error:4706)

int main()
{
    int a = 2;
    if (a = 3)  // Want a warning here
        std::cout << "Avoid this!\n";
}

现在给出：

错误 C4706：条件表达式内的赋值

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