C: signed integer sentinel value? -

i writing program wherein need turn character array integer. however, instead of using positive integers, need utilize full potential of integers (in range of capability of type int of course) (i.e: positive, negative, , 0). need access sentinel value, very so preferably within type int. don't want have make float can use 1 noninteger sentinel, if can avoid it.

to solve problem temporarily, i've been using following "trick": (where token array)

int tokentoint(char token[]) {     int current=0, value=0;     char isneg = 'f';      if (token[current] == '-') {         isneg = 't';         current++;     }      while (1) {         if (isdigit(token[current]) == 0)             return -1;         else {             value *= 10;             value += token[current]-'0';         }          current++;     }      if (isneg == 'f') return value;     if (isneg == 't') return -1 * (value + 1); } 

so in rest of program, use -1 error checking, , once you're done that, increment returned value if it's negative. works, except possibly if user inputs -2^15, better not able input -1, right?

but it's cumbersome, , kind of confusing randomly increment value out of blue. should stick ^ method or there alternative accomplishes same task? if there alternative, alternative?

if red correctly, you're saying need return int, need able detect error. there 2 common ways of doing this: putting return value in argument passed reference, or adding method set/get errors.

for first, like

int myfcn(int* result, char[] input) {     // stuff     ...     if( success ) {         *result = ...;         return error_success;     } else {         return error;     } } 

the second like...

void caller() {     int value = tokentoint(...);     if( getlasterror() != error_success ) {         // handle error     } }  int tokentoint(...) {     // stuff     if( error ) {         setlasterror(error_whatever);         return result     }     return result; } 

you can getlasterror function additional details.