What C Standard Does g Default To?

Which C Standard Is the Default for g ?

A recent compilation error encountered while attempting to compile a C code has raised the question of what the default C standard is when using the g compiler. The code involved includes file stream and string manipulation. When compiled using the command 'g example.cpp', the compilation failed due to errors involving conversion between strings and const char*. However, using the command 'g -std=c 17 example.cpp' resolved the issue.

To investigate the default standard used by g when the -std flag is not specified, a method is presented to determine the default version of the C standard supported by a particular version of g :

Determining Default Standard

1. Bash: Execute the following command:

   g++ -dM -E -x c++ /dev/null | grep -F __cplusplus

2. PowerShell: Run the following command:

   g++ -dM -E -x c++ NUL | Select-String __cplusplus

   The output of these commands will display a line similar to:

   #define __cplusplus 199711L

   The value following '__cplusplus' indicates the default C standard version. In this example, it is C 98 (199711).

Practical Considerations

As a programmer, the decision of whether or always specify the -std flag depends on several factors:

• Project Requirements: If the project requires a specific C standard, it should be explicitly set using the -std flag.
• Compiler Version: Modern versions of g (4.7 ) support a wider range of C standards. If using an older version, specifying the -std flag may be necessary.
• Code Portability: If the code is intended to be portable across different compilers or platforms, it is best practice to explicitly specify the desired C standard to ensure consistent behavior.

In general, it is recommended to specify the C standard explicitly using the -std flag to avoid unexpected behavior due to implicit default settings. By controlling the C standard, programmers can ensure optimal performance, code correctness, and portability.

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