Check at runtime if macro was defined - c

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.

Answer 2

But, as this is Q&A-style article, I've found the solution.
The final result looks as follows:
TEST_BXI_MACRO_STRING(BXI_OS);
TEST_BXI_MACRO_STRING(BXI_ARCH);
TEST_BXI_MACRO_I32 (BXI_BITS);
TEST_BXI_MACRO_EXISTS_WEAK(BXI_ARCH_X32); // _WEAK as we don't need to fail
TEST_BXI_MACRO_EXISTS_WEAK(BXI_ARCH_X64);
The result:
Let us see every one of them closely
TEST_BXI_MACRO_STRING
This one is pretty simple:
#define TEST_BXI_MACRO_STRING(name) \
do \
{ \
print_macro_name(#name); \
if (!TEST_BXI_MACRO_DEFINED(#name, name(1))) \
print_macro_undefined_exit(); \
if (strlen(name "") == 0) \
print_macro_undefined_exit(); \
print_macro_value_string(name ""); \
} \
while (0)
We just using the idea that C allows const strings auto-concatenation. So when the macro exists we will receive
#define MACRO "Content"
"Content" "" = "Content"
and when it doesn't
"" = ""
Then we look at the length of the resulting string, and when it's 0 - bingo, macro is not defined. This will NOT work for "" macro, but this special case could be checked with TEST_BXI_MACRO_EXISTS
TEST_BXI_MACRO_I32
#define TEST_BXI_MACRO_I32(name) \
do \
{ \
print_macro_name(#name); \
if (!TEST_BXI_MACRO_DEFINED(#name, name(1))) \
print_macro_undefined_exit(); \
if ((5 * name + 1) == 5) \
print_macro_undefined_exit(); \
print_macro_value_signed(name + 0); \
} \
while (0)
NOTE: you can similarly create ...MACRO_U32 version just by replacing the printer formatter.
Here we use the fact that '+' operator could be unary AND binary.
Let us simulate three cases:
#define MACRO (10)
In this case the complete formula will look as follows:
5 * 10 + 1 => 50 + 1 => 51
#define MACRO (0)
In this case the multiplication fades out:
5 * 0 + 1 => 0 + 1 => 1
In some cases you can use this for additional check if the defined macro is 0 (like for preprocessing options and stuff)
#define MACRO
This case shows some math magic:
5 * + 1 => 5 * (+1) => 5 * 1 => 5
As +1 is interpreted as simple 1 we receive 5.
TEST_BXI_MACRO_EXISTS
#define TEST_BXI_MACRO_DEFINED_I(strstr, fnc) (strcmp(#fnc, strstr "(1)"))
#define TEST_BXI_MACRO_DEFINED(str, fnc) TEST_BXI_MACRO_DEFINED_I(str, fnc)
#define TEST_BXI_MACRO_EXISTS(name) \
do \
{ \
print_macro_name(#name); \
if (!TEST_BXI_MACRO_DEFINED(#name, name(1))) \
print_macro_undefined_exit(); \
else \
print_macro_defined(); \
} \
while (0)
This implementation uses the fact that the string value of macro should not expand same as its name (as #define A A is useles)
Additional functions
For those who want the printing functions, here they are:
void print_macro_name(const char * name)
{
printf(" checking: %-20s: ", name);
}
void print_macro_undefined_exit(void)
{
printf("\033[1;31mUNDEFINED\033[0m\n");
exit(1);
}
void print_macro_defined(void)
{
printf("\033[1;33mDEFINED\033[0m\n");
}
void print_macro_undefined(void)
{
printf("\033[1;32mUNDEFINED\033[0m\n");
}
void print_macro_value_string(const char * value)
{
printf("\"%s\"\n", value);
}
void print_macro_value_signed(i32 value)
{
printf("%d\n", value);
}
void print_macro_value_unsigned(u32 value)
{
printf("%u\n", value);
}