dynamic - Conditionally replacing a C function at runtime -

is possible conditionally replace function @ runtime in c (in particular, function in dynamically loaded library)?

i know can use ld_preload or make function of same name, such as:

// silly example intercepting exit typedef void (*exit_func)(int code);  void exit(int code) {     exit_func orig_exit = (exit_func)dlsym(rtld_next, "exit");      nslog(@"exit called code %d!!!!", code);      orig_exit(code); } 

however, possible conditionally replace function, @ runtime, after program has loaded , running?

if(some_condition) {     swap_impementations(exit, my_exit); } 

edit: similar is possible swap c functions? specifically, trying intercept call function different library loaded operating system.

what means that, example, intercept exit() function stdlib, call exit() anywhere call implementation instead of original, example above, except controllable @ runtime.

there have been suggestions of hooking call overwriting original jump instruction, hoping doesn't require stomping on executable memory, perhaps there call in dynamic linker "re-link" function after program starts , point somewhere else?

use function pointer purpose.