#include <stdio.h> // fprintf(), NULL #include <stdlib.h> // exit(), EXIT_SUCCESS #include <string.h> #include <dlfcn.h> #include <crt_externs.h> #include <mach-o/dyld_priv.h> int foo() { return 0; } int alt_foo() { return 10; } static const struct dyld_interpose_tuple sTable[] = { {&alt_foo, &foo} }; __attribute__((constructor)) void init() { // switch main executable to use alt_foo() when it calls foo() dyld_dynamic_interpose((const struct mach_header*)_NSGetMachExecuteHeader(), sTable, 1); }