Where's the problem?

  ~ $ cat sizeofmacro.c
  #include <stdio.h>

  #define pintsize(T) printf("sizeof(%s) is %zu. Big or small? You decide.\n", #T, sizeof(T))

  int main(int argc, char **argv) {
          pintsize(int);
          pintsize(argv);
          return 0;
  }
  ~ $ gcc sizeofmacro.c && ./a.out
  sizeof(int) is 4. Big or small? You decide.
  sizeof(argv) is 8. Big or small? You decide.

the preprocessor isn't evaluating it, it's just pasting the tokens in

the preprocessor doesn't know anything about structs or types

I was curious, too. Looked it up. Still don't understand tho.

>The sizeof in C is an operator, and all operators have been implemented at compiler level; therefore, you cannot implement sizeof operator in standard C as a macro or function. You can do a trick to get the size of a variable by pointer arithmetic.

Do you mean preprocessor directives?

I've got a colleague that would've double down on it as well...

You can use sizeof() in macros but not in #if expressions.

Yeah, I meant #if directives, like static_assert. I asked it to help me statically verify my assumptions about the ELF format and it gave me some pretty insane code. Here's the excerpt:

> Certainly, you can use a combination of sizeof and #error directives for conditional compilation to achieve a similar effect without static_assert.

  // Compile-time check for structure sizes
  #if sizeof(Elf32_Phdr) != sizeof(((Elf32_Ehdr*)0)->e_phentsize)
      #error "32-bit structure size mismatch"
  #endif

  #if sizeof(Elf64_Phdr) != sizeof(((Elf64_Ehdr*)0)->e_phentsize)
      #error "64-bit structure size mismatch"
  #endif

> In this example, if the structure sizes don't match, the preprocessor will generate an error at compile time using the #error directive.

> I didn't know sizeof could be used with the C preprocessor

> Yes, sizeof can be used in certain contexts within the C preprocessor.

> It's commonly employed in combination with the #if and #error directives to perform compile-time checks on sizes or other constants.

> This usage allows you to catch potential issues during compilation rather than at runtime.

I should probably go sleep a bit before I embarrass myself any further. After nearly 24 hours awake it seems I have lost the ability to tell macros and directives apart.

[delayed]