Visual C++ 2010 Express C2099 Error for structures initialized with constants in a macro

Compiler: Microsoft Visual C++ 2010 Express, SP1 Project Property: C/C++ Advance Compile As: Compile as C Code (/TC)

Message:

error C2099: initializer is not a constant

Simple Test Case Showing Error:

typedef struct
{
    char *stringP;
    int  lino;
} foo_t;


#define bad {static foo_t foo ={__FILE__,__LINE__};}
#define good {static foo_t fo开发者_StackOverflow中文版o ={"filename",10};}

int main()
{

    bad;        // error C2099: initializer is not a constant
    good;       // no error

    return 0;
}

This generates a C2099 error. This code compiles & links correctly under gcc but not Visual C++ 2010 Express (compile as C Code - i.e. /TC option).

Your code compiles well on my system (MS Visual Studio 2005).

You can preprocess your code to try finding the problem manually:

cl your_file.c /E > stuff.c

This generates a preprocessed file (you probably have to supply a whole lot more command-line options; you can copy-paste them from the project's Property Pages).

cl stuff.c

This should reproduce the problem. Then try looking at the code in stuff.c; if you don't see the problem immediately, try tweaking it (e.g. replacing complex things with 0) - this should hint on the problem.

(Since your system is much newer than mine, some details may be different, e.g. maybe the compiler on your system is called something other than cl, but the idea will probably work)

For some reason the Microsoft C compiler does not recognize the __LINE__ preprocessor macro as a constant (presumably because it changes from line to line?), so you can't use it to initialize a structure member.

Generating the preprocessed .i file doesn't really help because it generates legal code that compiles just fine after __LINE__ has been replaced with a constant. Apparently, the C compiler is not trying to compile this same preprocessed output.

You should be able to use

foo.lino = __LINE__;

later without any problems. This seems to be a gripe from the Microsoft C compiler. Other C compilers I've used don't seem to have any problems with this use of __LINE__.

The only workaround I've been able to find is to compile the file as C++ code (/Tp).

__LINE__ macro is not recognized as constant by MSVC compiler when "Edit & Continue" debug database mode is enabled. If you don't care about "Edit & Continue", you can switch to another database mode and the problem should disappear.