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Asked: 2026-05-16T21:27:48+00:00

According to the documentation for fgets() , the function takes three parameters: char *

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According to the documentation for fgets(), the function takes three parameters:

  • char * – a string that will hold the input
  • int – an integer that represents the maximum number of characters to read
  • FILE * – a FILE * to the stream to read from

I have no trouble calling the function. I just push the three parameters onto the stack, call the function, and increase ESP by 12.

My problem is with parameter #3. What should be passed in as the FILE * for standard input? In C, I can just use stdin, but I don’t know what the equivalent is in x86 assembly.

Update: I’m using NASM on Linux.

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1 Answer

  1. Editorial Team

    The problem with stdin is that it’s a macro that expands to something not only platform-specific, but most likely difficult to access from assembly by hand. If you’re willing to sacrifice stdio and use POSIX calls instead, stdin is the same as the well-known file descriptor #0. You can therefore pass 0 to read and get almost what you were looking for. I’m pretty sure this is more assembler-friendly than the stdin C macro.

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