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Checking overflow long long in C

I want to check variable from fgets isn't overflowing ling long int in C language. I tried this:

long long x; 
fgets(...)
...
if(x <= LLONG_MAX && x >= LLONG_MIN)

but it is not working because long long int will receive too large number; it goes back to LLONG_MIN + excess (I think so).

Solution

  • Use strtoll when you are trying to convert from char* to long long. These lines are take from strtoll documentation (strtoll) :

    The strtol() function returns the result of the conversion, unless the value would underflow or overflow. If an underflow occurs, strtol() returns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both cases, errno is set to ERANGE. Precisely the same holds for strtoll() (with LLONG_MIN and LLONG_MAX instead of LONG_MIN and LONG_MAX).