My program has AddressSanitizer error but I'm not sure how to read it

Question

I'm relatively new to C and just finished a train station schedule program that looks for the nearest time departing time, from a schedule file, relative to the user input time, source, and destination. The restrictions were no string.h and no dynamic memory allocation of any kind. The program worked fine when I tested it but when marked, it produced AddressSanitizer errors which we haven't learned yet. I'm not sure how to read the error code. The Following is my code:

#include <stdio.h>
#include <stdlib.h>

#define lineSize 4096

int main(int argc, char* argv[]) {

if(argc != 4){
    printf("Please provide <source> <destination> <time> as command line arguments\n");
    return(0);
}

int c = 0;
while(argv[3][c] != 0){
    c++;
}
if(c < 8){
    printf("Please enter a proper time\n");
    return(0);
}

char line[lineSize];
FILE * fpointer = fopen("timetable.list", "r");

int i;
int j;

int StartSize;
int DestinationSize;
int DepartTime;

for(StartSize = 0; argv[1][StartSize] != '\0'; StartSize += 1){
    continue;
}

for(DestinationSize = 0; argv[2][DestinationSize] != '\0'; DestinationSize += 1){
    continue;
}

for(DepartTime = 0; argv[3][DepartTime] != '\0'; DepartTime += 1){
    continue;
}

int hour = 23;
int min = 59;
int sec = 59;
int check = 1;
int matchStart = 0;
int matchEnd = 0;
int checkNearestTime = 0;
int isThereATime = 0;

while(fgets(line, lineSize, fpointer) != NULL){
    check = 1;

    for(i = 0; i < StartSize; i++){
        if(argv[1][i] == line[i]){
            matchStart = 1;
            continue;
        }
        else{
            check = 0;
            matchStart = 0;
        }
    }

  
    if(check == 1){
        i = 0;
        int j = StartSize + 2;

        while(i < DestinationSize){
            if(argv[2][i] == line[j]){
                i += 1;
                j += 1;
                matchEnd = 1;
            }
            else{
                check = 0;
                matchEnd = 0;
                break;
            }
        }
    }


    if(check == 1){
        i = 0;
        j = StartSize + DestinationSize + 4;
        while(i < DepartTime){
            if(argv[3][i] == line[j]){
                i += 1;
                j += 1;
            }
            else{
                check = 0;
                break;
            }
        }
        if(check == 1){
            printf("The next train to %s from %s departs at %s\n", argv[2], argv[1], argv[3]);
            return 0;
        }

        if(check == 0){
            j = StartSize + DestinationSize + 4;
            int lineFullHour = (line[j] - '0') * 10 + (line[j+1] -'0');
            int lineFullMin = (line[j+3] - '0') * 10 + (line[j+4] -'0');
            int lineFullSec = (line[j+6] - '0') * 10 + (line[j+7] -'0');
            int argvHour = (argv[3][0] - '0') * 10 + (argv[3][1]-'0');
            int argvMin = (argv[3][3] - '0') * 10 + (argv[3][4] -'0');
            int argvSec = (argv[3][6] - '0') * 10 + (argv[3][7] -'0');
                          
            if(lineFullHour > argvHour){
                if(lineFullHour < hour){
                    hour = lineFullHour;
                    min = lineFullMin;
                    sec = lineFullSec;
                    checkNearestTime = 1;
                }
                else if(lineFullHour == hour){
                    if(lineFullMin < min){
                        min = lineFullMin;
                        sec = lineFullSec;
                        checkNearestTime = 1;
                    }
                    else if(lineFullMin == min){
                        if(lineFullSec < sec){
                            sec = lineFullSec;
                            checkNearestTime = 1;
                        }
                    }
                }
            }

            else if(lineFullHour == argvHour && lineFullMin > argvMin){
                if(lineFullHour < hour){
                    hour = lineFullHour;
                    min = lineFullMin;
                    sec = lineFullSec;
                    checkNearestTime = 1;
                }
                else if(lineFullHour == hour){
                    if(lineFullMin < min){
                        min = lineFullMin;
                        sec = lineFullSec;
                        checkNearestTime = 1;
                    }
                    else if(lineFullMin == min){
                        if(lineFullSec < sec){
                            sec = lineFullSec;
                            checkNearestTime = 1;
                        }
                    }
                }
            }

            else if(lineFullHour == argvHour && lineFullMin == argvMin && lineFullSec > argvSec){
                if(lineFullHour < hour){
                    hour = lineFullHour;
                    min = lineFullMin;
                    sec = lineFullSec;
                    checkNearestTime = 1;
                }
                else if(lineFullHour == hour){
                    if(lineFullMin < min){
                        min = lineFullMin;
                        sec = lineFullSec;
                        checkNearestTime = 1;
                    }
                    else if(lineFullMin == min){
                        if(lineFullSec < sec){
                            sec = lineFullSec;
                            checkNearestTime = 1;
                        }
                    }
                }
            }

        }
    }

    if(matchStart == 1 && matchEnd == 1 && checkNearestTime == 1){
        isThereATime = 1;
    }

}

if(isThereATime == 1){
    
    printf("The next train to %s from %s departs at %02d:%02d:%02d\n", argv[2], argv[1], hour, min, sec);
    return 0;
}
if(isThereATime == 0){
    printf("No suitable trains can be found\n");
    return 0;
}

return 0;
}

Answer 1

The source code (line 53) and your report do not match (line 59) do not match. It complains about a NULL pointer, per @kaylum, that only happens if fpointer is NULL. In turn this means │FILE * fpointer = fopen("timetable.list", "r"); failed. Always implement error checking:

#include <errno.h>
#include <string.h>

...

FILE * fpointer = fopen("timetable.list", "r");
if(!fpointer) {
  fprintf(stderr, "fopen failed with %s", strerror(errno)));
  exit(1);
}