How to define a string literal in gcc command line

问题:

In gcc command line, I want to define a string such as -Dname=Mary, then in the source code I want printf("%s", name); to print Mary.
How could I do it?

回答1:

Two options. First, escape the quotation marks so the shell doesn't eat them:

gcc -Dname=\"Mary\"

Or, if you really want -Dname=Mary, you can stringize it, though it's a bit hacky.

#include <stdio.h>

#define STRINGIZE(x) #x
#define STRINGIZE_VALUE_OF(x) STRINGIZE(x)


int main(int argc, char *argv[])
{
    printf("%s", STRINGIZE_VALUE_OF(name));
}

Note that STRINGIZE_VALUE_OF will happily evaluate down to the final definition of a macro.

回答2:

to avoid the shell "eating" the quotes and other characters, you might try single quotes, like this:

gcc -o test test.cpp -DNAME='"Mary"'

This way you have full control what is defined (quotes, spaces, special characters, and all).

回答3:

Most portable way I found so far is to use \"Mary\" - it will work not only with gcc but with any other C compiler. For example, if you try to use /Dname='"Mary"' with Microsoft compiler, it will stop with an error, but /Dname=\"Mary\" will work.

回答4:

In Ubuntu I was using an alias that defines CFLAGS, and CFLAGS included a macro that defines a string, and then I use CFLAGS in a Makefile. I had to escape the double quote characters and as well the \ characters. It looked something like this:

CFLAGS='" -DMYPATH=\\\"/home/root\\\" "'

回答5:

FYI: Apparently even different versions of the same toolchain on the same system can act differently in this regard... (As in, it would seem this would be a shell-passing issue, but apparently it's not limited to merely the shell).

Here we have xc32-gcc 4.8.3 vs. (avr-)gcc 4.7.2 (and several others) using the same makefile and main.c, the only difference being 'make CC=xc32-gcc', etc.

CFLAGS += -D'THING="$(THINGDIR)/thing.h"' has been in-use on many versions of gcc (and bash) over several years.

In order to make this compatible with xc32-gcc (and in light of another comment claiming that \" is more portable than '"), the following had to be done:

CFLAGS += -DTHING=\"$(THINGDIR)/thing.h\"

ifeq "$(CC)" "xc32-gcc"
CFLAGS := $(subst \",\\\",$(CFLAGS))
endif

to make things really confusing in discovering this: apparently an unquoted -D with a // results in a #define with a comment at the end... e.g.

THINGDIR=/thingDir/ -> #define /thingDir//thing.h -> #define /thingDir

(Thanks for the help from answers here, btw).

回答6:

Here is a simple example:

#include <stdio.h>
#define A B+20 
#define B 10
int main()
{
    #ifdef __DEBUG__
        printf("__DEBUG__ DEFINED\n");
        printf("%d\n",A);
    #else
        printf("__DEBUG__ not defined\n");
        printf("%d\n",B);
    #endif
    return 0;
}

If I compile:

$gcc test.c

Output:

__DEBUG__ not defined
10

If I compile:

$gcc -D __DEBUG__ test.c

Output:

__DEBUG__ defined
30

回答7:

This is my solution for : -DUSB_PRODUCT=\""Arduino Leonardo\""
I used it in a makefile with:
GNU Make 3.81 (from GnuWin32)
and
avr-g++ (AVR_8_bit_GNU_Toolchain_3.5.0_1662) 4.9.2

The results in a precompiled file (-E option for g++) is:
const u8 STRING_PRODUCT[] __attribute__((__progmem__)) = "Arduino Leonardo";