cant free dynamic matrix

Question

As a part of my homework with C, I had to make a function which splits a string to all the words starting with the key(which is a letter) inserted. Everything works great except for the free function, When I try to free the dynamic matrix by function (rows and then skeleton) I get an error that the program has triggered a breakpoint.

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

char **Split(char *str, char letter, int *size);
void free_mat(char **mat, int size);

int main() {
    int size, i;
    char letter;
    char STR[100];
    char **strings_arr;
    printf("Please enter a string:\n");
    flushall;
    gets(STR);
    printf("Please enter a letter for a check:\n");
    letter = getchar();
    strings_arr = Split(STR, letter, &size);

    if (size > 0) {
        printf("The number of words that starts with the letter '%c' in the string '%s' is: %d\n\n", letter, STR, size);
    }
    printf("The words are:\n");
    for (i = 0; i < size; i++) {
        printf("%d . %s\n", i+1,strings_arr[i]);
    }
    free_mat(strings_arr, size);
    return 0;
}

void free_mat(char **mat, int size)  
{
    int i;
    for (i = 0; i < size; i++)
    {
        free(mat[i]);
    }
    free(mat);
}
char **Split(char *str, char letter, int *size) {
    int rows = 0, i, lengh = 0, j = 0, n = 0, m;
    char **strings_array;

    if ((str[0] == letter) || (str[0] == letter + 32) || str[0] == letter - 32) {
        rows++; 
    }
    for (i = 0; str[i] != '\0'; i++) {
         if (str[i] == ' ') {   
            if ((str[i + 1] == letter) || (str[i + 1] == letter + 32) || str[i + 1] == letter - 32) {
                rows++; 
            }
        }
    }
    if (rows == 0) {    
        printf("There are no words starting with '%c' letter in this string\n\n", letter);
    }
    i = 0;
    strings_array = (char*)malloc(rows * sizeof(char)); 
    if ((str[0] == letter) || (str[0] == letter + 32) || str[0] == letter - 32) { 
        while (str[i] != ' ' && str[i] != '\0') {
            lengh++;
            i++;
        }
        strings_array[j] = (char*)malloc((lengh + 1) * sizeof(char)); 
        for (n = 0; n < lengh; n++) {
            strings_array[j][n] = str[n];
        }
        strings_array[j][n] = '\0';
        j++;    
    }
    for (i = 1; str[i] != '\0'; i++) {
            if (letter == str[i] || letter == str[i] - 32 || letter == str[i] + 32) {
                lengh = 0;
                //k = 0;
                m = i;  
                while (str[m] != ' ' && str[m] != '\0') {
                    lengh++;
                    m++;
                }
                strings_array[j] = (char*)malloc(lengh + 1);    

                for (n = 0; n < lengh; n++) {
                    strings_array[j][n] = str[i++]; 
                }
                strings_array[j][n] = '\0';
                j++;    
            }
    }
    *size = rows;   // sends back the number of words by referance
    return strings_array;
}

Thanks!

Answer 1

A breakpoint is something that you manually insert in the code from your IDE or equivalent. It is used for debugging. When you run the code it is intended to stop when it reaches a breakpoint. So just remove the breakpoint and it should work as expected.

Note: Remove only the breakpoint. Not the code on that line.

You mentioned in comments below that you're using Visual Studio 2015. Here is the documentation for breakpoints in that software: https://learn.microsoft.com/en-us/visualstudio/debugger/using-breakpoints?view=vs-2019

But there are some other things about your code. First of all, use fgets instead of gets. Second, you seem to have posted the wrong version or something, because free_mat will not compile. However, that was easily solved by changing arr to mat.

There's also another error that xing mentioned in the comments. Change strings_array = (char*)malloc(rows * sizeof(char)) to strings_array = malloc(rows * sizeof(*strings_array)). The cast is not necessary, you picked the wrong type for the argument to sizeof and if you pass a dereferenced pointer instead of the type you'll save yourself a lot of problems in the future.