How to get rid of `deprecated conversion from string constant to ‘char*’` warnings in GCC?

Question

So I'm working on an exceedingly large codebase, and recently upgraded to gcc 4.3, which now triggers this warning:

warning: deprecated conversion from string constant to ‘char*’

Obviously, the correct way to fix this is to find every declaration like char *s = "constant string"; or function call like void foo(char *s); foo("constant string"); and make them const char pointers. However, that would mean touching 564 files, minimum, which is not a task I wish to perform at this point in time. The problem right now is that I'm running with -werror, so I need some way to stifle these warnings. How can I do that?

Answer 1

Sounds like you answered your own question.

Obviously, the correct way to fix this is to find every declaration like char *s = "constant string"; or function call like void foo(char *s); foo("constant string"); and make them const char pointers.

The compiler doesn't care if it's convenient for you to do it now.

Answer 2

I believe passing -Wno-write-strings to gcc will suppress this warning.

Answer 3

Check out gcc's Diagnostic Pragma support, and the list of -W warning options. Looks like gcc doesn't have an equivalent to VC++'s #pragma warning(disable:NNNN) support which is very useful for cases like this.

Answer 4

If it's an active code base, you might still want to upgrade the code base. Of course, performing the changes manually isn't feasible but I believe that this problem could be solved once and for all by one single sed command. I haven't tried it, though, so take the following with a grain of salt.

find . -exec sed -E -i .backup -n \
    -e 's/char\s*\*\s*(\w+)\s*= "/char const* \1 = "/g' {} \;

This might not find all places (even not considering function calls) but it would alleviate the problem and make it possible to perform the few remaining changes manually.

Answer 5

The problem right now is that I'm running with -Werror

This is your real problem, IMO. You can try some automated ways of moving from (char *) to (const char *) but I would put money on them not just working. You will have to have a human involved for at least some of the work. For the short term, just ignore the warning (but IMO leave it on, or it'll never get fixed) and just remove the -Werror.

Answer 6

Why don't you use the -Wno-deprecated option to ignore deprecated warning messages?

Answer 7

I had a similar problem, I solved it like this:

#include <string.h>
extern void foo(char* m);

int main() {
    // warning: deprecated conversion from string constant to ‘char*’
    //foo("Hello");

    // no more warning
    char msg[] = "Hello";
    foo(msg);
}

Is this an appropriate way of solving this? I do not have access to foo to adapt it to accept 'const char*', although that would be a better solution (because foo does not change m).

Answer 8

You can also create a writable string from a string constant by calling strdup().

For instance, this code generates a warning:

putenv("DEBUG=1");

However, the following code does not (it makes a copy of the string on the heap before passing it to putenv): putenv(strdup("DEBUG=1"));

In this case (and perhaps in most others) turning off the warning is a bad idea -- it's there for a reason. The other alternative (making all strings writable by default) is potentially inefficient.

Listen to what the compiler is telling you!

Answer 9

I can't use the compiler switch. So I have turned this:

char *setf = tigetstr("setf");

to this:

char *setf = tigetstr((char *)"setf");

Answer 10

"Test string" <- This is const string. So you can solve like this: char str[] = "Test string"; or const char* str = "Test string"; printf(str);

Answer 11

I got the WARNING with this code snippet with GCC compiler 4.3:

// WHY the following COMPILER WARNING ???
// "deprecated conversion from string constant to char *"
char *const name = "dennis";

My answer is that the right side is "char *", but the left side is "char *const", and they don't agree.

Thus we are trying to enforce constantness in the pointer in the assignment.