Simon Anciaux
1108 posts
How to do metaprogramming without changing the source files?
Replying to longtran2904 (#25524)

To print lots of new lines with printf you can create a string that contains only new lines and use the width specifier to select how many you want. But you need to be careful not to print more than what's in the string.

#define new_lines "\n\n\n\n\n\n\n\n\n\n"

assert( desired_new_lines <= sizeof( new_lines ) - 1 );

printf( "%.*s", desired_new_lines, new_lines );

73 posts
How to do metaprogramming without changing the source files?
Replying to mrmixer (#25530)

Wait, you can use sizeof on string? I don't even know that. I always thought you need to use something like strlen.

Simon Anciaux
1108 posts
How to do metaprogramming without changing the source files?

Only on string literals.

uintptr_t size = sizeof( "abc" ) - 1;
assert( size == 3 );

char* string = "abc";
uintptr_t size = sizeof( string );
assert( size == 8 ); /* Size of the pointer. */


You can build string + size with macro:

typedef struct string_t {
uintptr_t length;
uint8_t* bytes;
} string_t;

#define string_l( literal ) ( string_t ) { sizeof( literal ) - 1, ( literal ) }

string_t string = string_l( "some string" );

73 posts
How to do metaprogramming without changing the source files?

I'm trying to have function overloading in C. The first idea is to just do what C++ does: mangling the name. But if I do that, I don't think the function's name in the error code would be correct. Are there any directives that can help me here?

Mārtiņš Možeiko
2235 posts / 1 project
How to do metaprogramming without changing the source files?
Edited by Mārtiņš Možeiko on
Replying to longtran2904 (#25537)

I don't think there exists anything for that. If you change name, you'll have different name.

For function overloading there is another option you can do, if you use clang compiler - it has builtin support for overloading in C code with extra attribute on functions:

#define overload __attribute__((overloadable))

overload void fun(int x) { ... }
overload void fun(float x, float y) { ... }
// repeat for as many other arguments you want

73 posts
How to do metaprogramming without changing the source files?
Replying to mmozeiko (#25538)

Thanks! Did not know that.

498 posts
How to do metaprogramming without changing the source files?

There is also _Generic which lets you decide the logic of picking the overload:

//code from cppreference.com
#include <stdio.h>
#include <math.h>

// Possible implementation of the tgmath.h macro cbrt
#define cbrt(X) _Generic((X), \
long double: cbrtl, \
default: cbrt,  \
float: cbrtf  \
)(X)

int main(void)
{
double x = 8.0;
const float y = 3.375;
printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
printf("cbrtf(3.375) = %f\n", cbrt(y)); // converts const float to float,
// then selects cbrtf
}