How to set errno value?

Question

I have two calls to two different methods :

void func1()  {   // do something    if (fail)    {     // then set errno to EEXIST    }  } 

And the second method :

void func2()  {   // do something    if (fail)    {     // then set errno to ENOENT    }  } 

1. When I set the errno to some value , what does it do ? just error checking ?

2. How can I set errno in the above methods func1 and func2 to EEXIST and ENOENT

Thanks

Answer 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; 

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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 ?

Answer 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.