How to set errno value?
For all practical purposes, you can treat errno like a global variable (although it's usually not). So include errno.h and just use it:
errno = ENOENT;You should ask yourself if errno is the best error-reporting mechanism for your purposes. Can the functions be engineered to return the error code themselves ?
IMO, the standard errno designed for system level. My experience is do not pollute them. If you want to simulate the C standard errno mechanism, you can do some definition like:
/* your_errno.c */__thread int g_your_error_code;/* your_errno.h */extern __thread int g_your_error_code#define set_your_errno(err) (g_your_error_code = (err))#define your_errno (g_your_error_code)and also you can still implement your_perror(err_code). More information, please refer to glibc's implementation.
#include <errno.h>void func1() { // do something if (fail) { errno = ENOENT; }}