Why am I getting segmentation fault for this program? - c

Question

I have to write a program which reads dates and todo-s as command line arguments and puts these in a text-file (line by line).
Correct input:
./todo 13:58 todo1 00:00 todo2 08:30 todo3
Wrong input:
./todo 13:58 todo1 24:00 todo2 08:30 todo3 or ./todo 13:58 todo1 todo2 00:00 08:30 todo3
Correct todolist.txt file:
13:58 - todo1
00:00 - todo2
08:30 - todo3
The code is compiled successfully, but when I run the program, I get segmentation fault:
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
bool isValidTime(char* argv)
{
char hour[2] = {0};
char minute[2] = {0};
for (unsigned int i = 0; argv[i] != ':'; i++) {
hour[i] = argv[i];
}
int hourNum = atoi(hour);
if (!(hourNum >= 0 && hourNum < 24)) {
return false;
}
for (unsigned int i = 3; i < sizeof(*argv) / sizeof(argv[0]); i++) {
minute[i] = argv[i];
}
int minuteNum = atoi(minute);
if (!(minuteNum >= 0 && minuteNum < 60)) {
return false;
}
return true;
}
bool isValidTodo(char* argv)
{
for (unsigned int i = 0; i < sizeof(*argv) / sizeof(argv[0]); i++) {
if (!(argv[i] >= 'a' && argv[i] <= 'z')) {
return false;
}
}
return true;
}
int main(int argc, char* argv[])
{
if (argc < 3) {
printf("Incorrect input!\n");
return 1;
}
FILE* file;
file = fopen("todolist.txt", "w");
if (file == NULL) {
printf("File failed to open.\n");
return 1;
}
for (int i = 1; i < argc; i++) {
if (!(isValidTime(argv[2 * i - 1]) && isValidTodo(argv[2 * i]))) {
printf("Incorrect input!\n");
}
fprintf(file, "%s - %s\n", argv[2 * i - 1], argv[2 * i]);
}
fclose(file);
return 0;
}

Answer 1

Most likely it is because of this code:
for (int i = 1; i < argc; i++) {
if (!(isValidTime(argv[2 * i - 1]) && isValidTodo(argv[2 * i]))) {
printf("Incorrect input!\n");
}
fprintf(file, "%s - %s\n", argv[2 * i - 1], argv[2 * i]);
}
You are getting argc number of arguments, but then you index the array using argv[2 * i - 1]. Say you have 4 arguments - you are going to try to index element 2 * 4 - 1, that is, element 7 which would be outside the array, hence the segmentation fault.
You probably need to just remove the 2 * part, if your goal is to do something with the previous and current elements.
Another issue I see is this code:
for (unsigned int i = 0; argv[i] != ':'; i++) {
hour[i] = argv[i];
}
In case there is no : in the argument, you will loop indefinitely and will get another segmentation fault for hour[i] and argv[i].