Because the integer types have a fixed number of bits, they have fixed ranges. The number of bits assigned to an int is system dependent, which means that it could have a different number of bits on different systems. It looks like a short int is fixed at 16 bits and a long int at 32 bits, but I'm not sure that's really the case.
Since most of our work is with a 16-bit compiler, I'm used to an int being 16 bits long, such that a signed int's range is from –32,768 to 32,767 and an unsigned int is from 0 to 65,535. As you can see, your number is still beyond the range of the unsigned int. A long int (32-bit) ranges +/- 2.14 billion (+/- 2 G) or unsigned from 0 to 4.29 billion (4 G). Your number of 265 million will fit in a long int.
The long int version of atoi() is atol(), which returns a long int value. I didn't find a atoul, but there is also a family of strtoul(), etc, functions which appear to do the same thing as atoi & atol, but I'm not familiar with them and don't know how they differ.
Both atoi et al. and strtoi et al. appear to handle overflow the same way (trying to convert a number that exceeds the range of the data type); from the description of atoi:
RETURN VALUES |
The atoi() function returns the converted integer value.
If the converted value overflows, LONG_MIN or LONG_MAX is returned (according to the sign of the value) and errno is set to ERANGE. If no character could be converted, zero is returned.
Read the man/help page for the function you end up using for details.