CODEWITHSUNDEEP
clinuxgcc
Don Hall
Don Hall

Reputation: 107

gcc macro define option doesn't work for string

Sample code:

main()
{
    printf("%d\n", MARCO);  
//  printf("%s\n", MARCO);
}

When I try to use gcc -D option, I found the following command works:

gcc -D MARCO=12345 test.c

but when I change 12345 to a string:

gcc -D MARCO=abcde test.c

an error occurs:

error: ‘abcde’ undeclared (first use in this function)

I have tried -DMARCO=abcde, -DMARCO="abcde", -D MARCO="abcde"; all failed with that error.

Does this -D option only support integers?

Upvotes: 2

Views: 7145

Answers (3)

Confusion
Confusion

Reputation: 16841

The macro MARCO is literally replaced by the string you entered and only then is the code compiled. Since there are no quotes around the string (the double quotes in two of the examples are interpreted as delimiters by the shell), the abcde is not interpreted as a string, but as an identifier. Since it isn't defined, the code fails to compile.

Upvotes: 2

Adeel Ahmed
Adeel Ahmed

Reputation: 1601

you can also use like this...

-DMACRO="\"abcde\""

Ref: How do I pass a quoted string with -D to gcc in cmd.exe?

Upvotes: 2

Jonathan Leffler
Jonathan Leffler

Reputation: 753785

The trouble is that double quotes are recognized by the shell and removed, unless you prevent the shell from doing so by escaping the double quotes (with backslashes) or enclosing them in single quotes (which is what I'd use):

gcc -DMARCO='"abcde"' test.c

The single quotes are stripped by the shell but that means that the double quotes are seen by the C preprocessor. You need to use the %s format, of course.

By changing the macro, you can stringify a non-quoted name on the command line:

#include <stdio.h>
#define STRINGIFY(x) #x
#define MACRO(x)     STRINGIFY(x)
int main(void)
{
    printf("%s\n", MACRO(MARCO));
    return(0);
}

Compile that with gcc -o testprog -DMARCO=abcde test.c and you will find it produces the correct answer.

Upvotes: 16

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