Is atoi() part of C standard?

Question

Is atoi() part of C standard?

What should I use to convert char* to int if atoi() isn't standardised?

Answer 1

Yes, atoi() is part of standard C -- unfortunately.

I say "unfortunately" because it does no error checking; if it returns 0, you can't tell whether it's because you passed it "0" or because you passed it "hello, world\n" (which has may have undefined behavior, but typically returns 0).

The strtol() function is more complicated to use, but it does proper error checking. It returns a long result, which you can then convert to int -- ideally after checking that it's in the range INT_MIN to INT_MAX.

Reference: N1570 7.22.1.2.

Answer 2

It is part of the C Standard Library, and should be declared within stdlib.h

Answer 3

atoi is part of the current C standard but consider strtol which is also part of the standard and has a more robust interface.

Answer 4

Yes, it is standard. From man atoi:

NAME atoi, atoi_l -- convert ASCII string to integer

LIBRARY Standard C Library (libc, -lc)

#include <stdlib.h>

However, it also says:

The atoi() function has been deprecated by strtol() and should not be used in new code.