printf the contents of a file (documentation) at compile time

Question

The prolific way of printing documentation for hacky programs is generally:

void print_help(){
    printf("a whole bunch of information
            generally spanning many lines and looking ugly
            requires editing a c file to modify documentation");
}

This is ugly IMO, and doesn't make it easy to modify the documentation. The alternatives:

generally dismissive:

void print_help(){
    printf("read the README, you idiot");
}

error prone, complex:

void print_help(){
    fopen("readme.md", "r");
    //error check;
    while (read from file){
         printf("%s", line);
    }
}

I'd like to bridge the gap between solutions 1 and 3, namely:

void print_help(){
    printf("#include"help_file.txt"");
}

I guess my questions would be:

is it really this simple? Does the preprocessor jump over strings, or will it notice the include directive?
Potential issues? I know anything that won't printf nicely will cause issues if it's put in the files

Did you try to compile it? Yes, you can do something *like* this, but not the way you did. — Eugene Sh., Sep 13 '21 at 16:05
Preprocessor directives have to be at the beginning of the line (except for whitespace). And they're not processed inside strings. — Barmar, Sep 13 '21 at 16:06
@EugeneSh. I did try this, and any permutation of escape sequences failed. How would one do something _like_ this? Does the entire printf have to be in the text file? — Brydon Gibson, Sep 13 '21 at 16:09
Duplicate of https://stackoverflow.com/questions/43256465/include-a-file-as-a-string ? — KamilCuk, Sep 13 '21 at 16:11
@KamilCuk You're not wrong, however it seems the best answers to this are still in this question — Brydon Gibson, Sep 13 '21 at 16:14

score 1 · Accepted Answer · answered Sep 13 '21 at 16:09

1

Create an include file that defines the documentation as a variable.

help_file.h:

char *help_text = "
a whole bunch of information\n\
generally spanning many lines and looking ugly\n\
requires editing a c file to modify documentation"

program.c:

void print_help(){
    #include "help_file.h"
    printf("%s", help_text);
}

You can use a shell script to create the include file from a plain .txt file.

answered Sep 13 '21 at 16:09

Barmar

741,623
53
500
612

There must be some trick to use plain text file.. can't come up with one though – Eugene Sh. Sep 13 '21 at 16:20
Nope, not that I can think of. – Barmar Sep 13 '21 at 16:21
Yeah, probably with some extra scripts only – Eugene Sh. Sep 13 '21 at 16:21

score 0 · Answer 2 · answered Sep 13 '21 at 16:09

The contents of strings are not processed by the preprocessor, so you can't substitute the contents of a file with a string like that.

If you want the help file to be plain text that doesn't look like a series of C strings, your only option is to read the contents of an external file at run time and print it. And I wouldn't exactly call it error prone or complex:

void print_help()
{
    FILE *f = fopen("readme.md", "r");
    if (!f) {
        printf("can't print help file");
    } else {
        char line[500];
        while (fgets(line, sizeof line, f){
          puts(line);
        }
        fclose(f);
    }
}

What makes it error-prone is finding a reliable filepath for the first argument to `fopen("readme.md", "r");` — rici, Sep 13 '21 at 19:25

printf the contents of a file (documentation) at compile time

2 Answers2