How to parse dates in C?

Question

I'm having trouble with one of my assignments for my C class, the objective is to read the dates from input, parse the dates, and have them output in the m/d/yyyy format. I have most of the code done but I don't know which functions to use to look for the dates and output it in the correct format. I didn't type a printf function yet because I've been trying to get the input first. I also commented out some of the input to show what I've been having trouble with. Here is my code:

#include <stdio.h>
#include <string.h>

int GetMonthAsInt(char *monthString) {
    int monthInt;

    if (strcmp(monthString, "January") == 0) {
        monthInt = 1;
    }
    else if (strcmp(monthString, "February") == 0) {
        monthInt = 2;
    }
    else if (strcmp(monthString, "March") == 0) {
        monthInt = 3;
    }
    else if (strcmp(monthString, "April") == 0) {
        monthInt = 4;
    }
    else if (strcmp(monthString, "May") == 0) {
        monthInt = 5;
    }
    else if (strcmp(monthString, "June") == 0) {
        monthInt = 6;
    }
    else if (strcmp(monthString, "July") == 0) {
        monthInt = 7;
    }
    else if (strcmp(monthString, "August") == 0) {
        monthInt = 8;
    }
    else if (strcmp(monthString, "September") == 0) {
        monthInt = 9;
    }
    else if (strcmp(monthString, "October") == 0) {
        monthInt = 10;
    }
    else if (strcmp(monthString, "November") == 0) {
        monthInt = 11;
    }
    else if (strcmp(monthString, "December") == 0) {
        monthInt = 12;
    }
    else {
        monthInt = 0;
    }

    return monthInt;
}

int main() {

    // TODO: Read dates from input, parse the dates to find the ones
   //       in the correct format, and output in m/d/yyyy format
   char month = NULL;
   char day = NULL;
   char year = NULL; 
   char date = NULL;
   char dateFormat[100];
   int mm;
   int i;
   
   while(1) {
    getchar(dateFormat[100], date);

   if(date == "-1")
     break;
     
  // int length = strlen(date); //
  // int dateFormat2 = date.(" ");  //
  //   month = .(mm); //
  //   day = date.; //
  //  year = date. //
  //  month = date; //
 //   mm = .(month); //

 
   if(date[length - 6] == ',' && mm > 0) {
     dateFormat[i++] = month + "//" + day + "//" + year;
    }
  }
    return 0;
}

Answer 1

Here is an example implementation that Jonathan Leffler suggested above. This assumes newline terminated dates, and I showed a couple of example formats (you may need to expand this to match your data):

#include <stdio.h>
#include <string.h>
#include <time.h>

#define LEN 100

int main() {
    for(;;) {
        char s[LEN] = {0};
        fgets(s, LEN, stdin);
        if(!strcmp(s, "-1"))
            break;
        const char *formats[] = {
            "%h %d, %Y",
            "%m/%d/%Y",
        };
        struct tm tm = { 0 };
        for(unsigned i = 0; i < sizeof(formats) / sizeof(*formats); i++) {
            char *s2 = strptime(s, formats[i], &tm);
            if(s2 && *s2 == '\n') {
                // or use strftime()
                printf("%u/%u/%u\n",
                    tm.tm_mon + 1,
                    tm.tm_mday,
                    tm.tm_year + 1900
                );
                break;
            }
        }
    }
    return 0;
}

Consider printing out failed dates, say, to stderr, so you can tweak your formats.