Check at runtime if macro was defined

Question

During the developing of static library I met the necessity to test the library functions. The functions checks are not the problem. The main problem is to test every macro definition that the library provides.

I've started with the code like

/* For non-vital macro (OS/WORDSIZE detections) */
#   if defined(BXI_ARCH_X32)
    printf("        defined : BXI_ARCH_X32\n");
#   endif
#   if defined(BXI_ARCH_X64)
    printf("        defined : BXI_ARCH_X64\n");
#   endif

<...>

/* For vital macro */
#if defined(BXI_OS)
    printf("        defined : BXI_OS  : \"%s\"\n", BXI_OS);
#else
    print_failed();
#endif

#if defined(BXI_BITS)
    printf("        defined : BXI_BITS: %d\n",     BXI_BITS);
#else
    print_failed();
#endif

#if defined(BXI_ARCH)
    printf("        defined : BXI_ARCH: \"%s\"\n", BXI_ARCH);
#else
    print_failed();
#endif

That was cool, but very time-consuming. I wanted a tool that will generate the code for me, or some trick that will allow me to autogenerate the tests via macro like this

TEST_MACRO(BXI_OS)

But, as you know, macro definitions can't generate #if/#else/#endif directives.

I needed a solution that will not only check if the macro defined at runtime, but also print its value to output.

Answer 1

I've met a simillar problem and found another nice trick to implement your TEST_BXI_MACRO_EXISTS with no string.h and extra function calls:

#define STRINGIZE_I(x) #x
#define TEST_BXI_MACRO_EXISTS(name) (#name [0] != STRINGIZE_I(name) [0])

This trick uses the same assumption that stringized value of defined macro does not match stringized name of that macro. But for my case I only needed to check if macro is defined as a numeric constant, string literal or empty value. No function-like macros and other stuff.

This is how it works:

#define MACRO "Content"
TEST_BXI_MACRO_EXISTS(MACRO)
// translates to ("MACRO"[0] != "\"Content\""[0])
// first letter of a valid macro name can never be equal to '"'

#define MACRO 3.14
TEST_BXI_MACRO_EXISTS(MACRO)
// translates to ("MACRO"[0] != "3.14"[0])
// first letter of a valid macro name can never be equal to a digit

#define MACRO
TEST_BXI_MACRO_EXISTS(MACRO)
// translates to ("MACRO"[0] != ""[0])
// first letter of a valid macro name can never be equal to a '\0'

This approach can also be easily used to test whether macro defines a numeric constant, string literal or empty value like your approach does by checking the value of STRINGIZE_I(name) [0].

So far I have no idea how to test function-like macros this way, but I thought sharing this with others could be useful anyway.