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Compiler Warning (level 4, no longer emitted) C4001

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nonstandard extension 'single line comment' was used

Note

This warning is removed in Visual Studio 2017 version 15.5 because single-line comments are standard in C99.

Single-line comments are standard in C++ and standard in C starting with C99. Under strict ANSI compatibility (/Za), C files that contain single-line comments, generate C4001 due to the usage of a nonstandard extension. Since single-line comments are standard in C++, C files containing single-line comments don't produce C4001 when compiling with Microsoft extensions (/Ze).

Example

To disable warning, uncomment #pragma warning(disable:4001).

// C4001.cpp
// compile with: /W4 /Za /TC
// #pragma warning(disable:4001)
int main()
{
   // single-line comment in main
   // C4001
}