Problem with a text macro.

Hi,

Just found out about preprocessor macros, and was trying to create a popen command that would include a changing directory.

I tried the following:

Code:

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#define COMMAND(dir) "find " #dir " -type f -printf '%T@ %t %p\\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev"

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And it does what I need with the following:

Code:

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printf("%s\n", COMMAND("/home/user/directory"));

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But I'm now trying to use a '#define' as the argument for the macro, but it just uses the NAME rather than the value:

Code:

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printf("%s\n", COMMAND(DIRECTORY));

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Prints:

Code:

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find DIRECTORY -type f -printf '%T@ %t %p\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev

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Instead of:

Code:

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find "/home/user/directory" -type f -printf '%T@ %t %p\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev

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What am I doing wrong? Is this even possible?

Something like this?

Code:

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#define STR(x)  #x
#define COMMAND(dir) "find " STR(dir) " -type f -printf '%T@ %t %p\\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev"
#define DIRECTORY /home/user/directory

int main ( ) {
  printf("%s\n", COMMAND(DIRECTORY));
}



$ gcc -E main.c
# 1 "main.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "main.c"
int main ( ) {
  printf("%s\n", "find " "/home/user/directory" " -type f -printf '%T@ %t %p\\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev");
}

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Yes, that worked, but I found the following:

Code:

---

#define COMMAND(dir) "find " dir " -type f -printf '%T@ %t %p\\n' | sort -k 1 -nr | rev | cut -d' ' -f1 | rev"

---

Includes the double quotes around the directory name (which I wasn't really concrened with, but is nice to have). It's without the pound symbol (#).

Other than the double quotes being included, is there anything I need to be aware of if I choose to use "dir" without the preceeding pound symbol. Or is it safer to use STR(dir)?

I'd say that it makes more sense to #define DIRECTORY to be a string literal instead of a token that you then stringify: that way, if you want to say print DIRECTORY for some reason, you just do it. So yes, that combined with the direct approach of making use of the automatic concatenation of adjacent string literals is sensible.