Is it possible to turn "-Wwrite-strings" into an error? - gcc

Question

I've tested this on GCC 4.8.3, 4.9.2 and trunk 20141210. When using -Werror=write-strings, it correctly enables the warning, but doesn't turn it into an error. The command line I'm using is:
g++ -std=c99 -x c -Werror=write-strings -O2 -Wall -pedantic main.cpp
warning: initialization discards 'const' qualifier from pointer target type
char *s = "test";
However, it turns it into an error in C++ mode:
g++ -Werror=write-strings -O2 -Wall -pedantic -pthread main.cpp
main.cpp:8:15: error: deprecated conversion from string constant to 'char*'
[-Werror=write-strings]
char *s = "test";
Is there something I'm missing or is this just a missing feature?

Answer 1

I've seen the deleted answer, but bear with me…it was actually correct (at least, under my testing). I think what you've found is interesting, and close to being a bug.
As far as my testing goes (GCC 4.9.1 built on Mac OS X 10.9.4 Mavericks, running on Mac OS X 10.10.2 Yosemite), it appears that the -Werror=write-strings does not make the warning into an error (which I regard as being probably a bug, though you may find that the GCC team has a different view on it). It only becomes an error when -Werror is in effect.
Here's what I ran:
$ cat x.c
#include <stdio.h>
int main(void)
{
char *test = "data";
printf("%s\n", test);
return 0;
}
$ gcc -O3 -g -std=c11 -c x.c
$ gcc -O3 -g -std=c11 -c x.c -Wwrite-strings
x.c: In function ‘main’:
x.c:5:18: warning: initialization discards ‘const’ qualifier from pointer target type
char *test = "data";
^
$ gcc -O3 -g -std=c11 -c x.c -Werror=write-strings
x.c: In function ‘main’:
x.c:5:18: warning: initialization discards ‘const’ qualifier from pointer target type
char *test = "data";
^
$ gcc -O3 -g -std=c11 -c x.c -Werror -Wwrite-strings
x.c: In function ‘main’:
x.c:5:18: error: initialization discards ‘const’ qualifier from pointer target type [-Werror]
char *test = "data";
^
cc1: all warnings being treated as errors
$ gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror=write-strings
x.c: In function ‘main’:
x.c:5:18: warning: initialization discards ‘const’ qualifier from pointer target type
char *test = "data";
^
$ gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror
$ gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror -Wwrite-strings
x.c: In function ‘main’:
x.c:5:18: error: initialization discards ‘const’ qualifier from pointer target type [-Werror]
char *test = "data";
^
cc1: all warnings being treated as errors
$ gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror -Werror=write-strings
x.c: In function ‘main’:
x.c:5:18: error: initialization discards ‘const’ qualifier from pointer target type [-Werror]
char *test = "data";
^
cc1: all warnings being treated as errors
$
For your convenience, and for easier viewing, these are the GCC commands I ran:
gcc -O3 -g -std=c11 -c x.c
gcc -O3 -g -std=c11 -c x.c -Wwrite-strings
gcc -O3 -g -std=c11 -c x.c -Werror=write-strings
gcc -O3 -g -std=c11 -c x.c -Werror -Wwrite-strings
gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror=write-strings
gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror
gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror -Wwrite-strings
gcc -O3 -g -std=c11 -c x.c -Wall -Wextra -Werror -Werror=write-strings
If you can't run with -Werror normally, then you're probably going to have to do trial builds with -Werror -Wwrite-strings which will fail because of other problems, but this will also identify the writable strings problems, which you can fix and check. Then, when you're OK on the -Wwrite-strings errors, you can go back to not including -Werror in the compilation (keeping -Wwrite-strings or even -Werror=write-strings in the command line so that if you make a mistake and/or the putative compiler bug is fixed, then you can have it all working the way you really wanted).