How to set errno value?

Solution 1:

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 ?

Solution 2:

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.