How to compile C code on Linux/GCC without deprecated functions being available?

Question

There are old functions such as index, rindex which have now been superseded by strchr and strrchr.

Is there a way to configure the compiler or defines so these functions aren't available?

It can cause confusing warnings when:

• accidentally using index name outside of scope for eg - or worse, not warn and use the function in a way that's not intended.
• Older GCC versions (4.x) warn when using -Wshadow if you have a variable called index.

See:

• http://www.gnu.org/software/libc/manual/html_node/Search-Functions.html#index-index
• http://pubs.opengroup.org/onlinepubs/009695399/functions/index.html

---

Notes:

• as @antti-haapala says, the global symbol index shouldn't be redefined since libraries may use it.
  This question is regarding the common case when a local variable is called index.
• At the time of writing, glibc doesn't mark these functions with the deprecated attribute, so warnings related to using deprecated functions have no effect.

Answer 1

Use the compiler in ISO C mode. The C standard prohibits conforming programs being broken by the presence of identifiers that are not reserved words.

For example, use flags -std=c99.

Sample program:

#include <string.h>

int main()
{
   index("abc", 'x');
}

Compiled with -std=c11 -Werror gives:

error: implicit declaration of function 'index' [-Werror=implicit-function-declaration]

Answer 2

You shouldn't redefine these identifiers, as some library that you're linking against could still depend on them existing.