How to check a specific format of string in C - c

Question

I have the following code that accepts a string that resembles hours.. I want to check if the string format is actually xx-yy where xx resembles an hour as does yy.. The code worked fine but when I input "02-13-" it returns true but I want it to return false cause it's not correct (cause it has - at the end)
bool hourIsValid(char * hours) {
int openH = 0;
int closeH = 0;
if ((sscanf(hours, "%d-%d", & openH, & closeH) == 2) && openH >= 0 && openH <= 24 && closeH >= 0 && closeH <= 24) {
if (openH >= closeH) {
return false;
}
return true;
} else {
return false;
}
}

Answer 1

The solution depends on how "pedantic" your code has to be when deciding if an input is valid or not. For example, you might expect "2-14", "02 - 15", " 2-14 " as valid, or you might not. It depends.
If you want to get a pedantic version that accepts only the exact format "dd-dd" with no leading or trailing characters or white spaces and with exactly a two-digit format for each hour value, you could check the string as follows before reading in the values with your sscanf-code:
if (strlen(hours) != 5)
return 0;
if (hours[2] != '-')
return 0;
if ( !isdigit(hours[0])
|| !isdigit(hours[1])
|| !isdigit(hours[3])
|| !isdigit(hours[4])
)
return 0;

Answer 2

Another way:
#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
bool hourIsValid(
char *I__hours
)
{
long openH, closeH;
openH=strtol(I__hours, &I__hours, 10);
if( '-' != *I__hours // Ensure that there is a dash between the two numbers in the string.
|| 0 >= openH // Ensure that the 1st number in the string is non-negative.
|| 24 <= openH // Ensure that the 1st number in the string is 24 or less.
)
return(false);
++I__hours; // Skip over the dash between the two numbers.
closeH=strtol(I__hours, &I__hours, 10);
if( *I__hours // Ensure that there are no additional characters beyond the 2nd number.
|| 0 >= closeH // Ensure that the 2nd number in the string is non-negative.
|| 24 <= closeH // Ensure that the 2nd number in the string is 24 or less.
|| openH >= closeH // Ensure that the 1st number is less or equal to the 2nd number.
)
return(false);
return(true);
}