EXIT_FAILURE vs exit(1)?

Question

What's the difference? Which is preferred, or when should I use each one respectively?

Answer 1

exit(1) (usually) indicates unsuccessful termination. However, its usage is non-portable. For example, on OpenVMS, exit(1) actually indicates success.

Only EXIT_FAILURE is the standard value for returning unsuccessful termination, but 1 is used for the same in many implementations.

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So to summarize:
If you want to write perfectly portable code use,

EXIT_FAILURE for failure case. While,
You can use either exit(0) or EXIT_SUCCESS for success case.

Note that, EXIT_SUCCESS or 0 are both same.

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Reference:

C99 Standard: 7.20.4.3 The exit function
Para 5

Finally, control is returned to the host environment. If the value of status is zero or EXIT_SUCCESS, an implementation-defined form of the status successful termination is returned. If the value of status is EXIT_FAILURE, an implementation-defined form of the status unsuccessful termination is returned. Otherwise the status returned is implementation-defined.

Answer 2

For truly portable code, EXIT_FAILURE is preferred. The C standard only defines meaning for three values: EXIT_FAILURE, 0, and EXIT_SUCCESS (with 0 and EXIT_SUCCESS essentially synonymous).

From a practical viewpoint, most typical systems accept other values as well. If memory serves, Linux will let you return any 8-bit value, and Windows 16-bit values. Unless you honestly might care about porting to an IBM mainframe, VMS, etc., chances are you don't care about most of the systems that won't support at least 8-bit return values.