Thread: Help needed to debug

I wrote this code but cannot figure out the issues that arise when trying to compile.

Code:

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


int find_First_Letter (char **word_Array, int num_words); /*Function to find the first letter of a string*/


int main (void){
    FILE *in, *out;
    int num_words, num_letters, x, y;
    
    in = fopen("alphabetic_sort.dat", "r");
    out = fopen("alphabetic_sort.out", "w");
    
    if (in == NULL || out == NULL)       /*Check to see whether files can be openned or not*/
    {
        printf("Error opening files!\n");
        fclose(in);
        fclose(out);
        return -1;
    }


    char **wordArray, c = '\0';
    fscanf(in, "%d", &num_words);
    wordArray = (char*) malloc(num_words*sizeof(char));   /*Creates memory for every word*/
    for(x = 0; x<num_words; x++){
        fscanf(in, "%d ", &num_letters);
        (wordArray + x) = (char) malloc((num_letters + 1)*sizeof(char)); /*Creates memory for every letter in the word. +1 due to null character at the end*/
        for (y = 0; y < num_letters; y++)
        {
            while (!((c >= 'a' && c <= 'z') || c == '\n'))   
            {
                fscanf(in, "%c", &c);
            }
            if (c == '\n')
            {
                ((wordArray + x) + y) = '\0';  /*Sets newline to a null character*/
            }else{
                ((wordArray + x) + y) = c;
            }
            
            c = '\0';  /*c is set to a null character*/
        }
        
    }


    int word_index;
    char *sortedwordArray = (char) malloc(num_words * sizeof(char));  /*Memoery is allocated according to the number of words inputted*/
    
    for (x = 0; x < num_words; x++)
    {
        word_index = find_First_Letter(wordArray, num_words);
        sortedwordArray[x] = wordArray[word_index];
        wordArray[word_index] = NULL
    }
    
    for (x = 0; x < num_words; x++)
    {
        fprintf(out, "%s\n", sortedwordArray[x]); /*Output gets printed to the required file*/
    }
    
    for (x = 0; x < num_words; x++)
    {
        free(*(wordArray + x));  /*Frees the memory preventing memory leaks*/
    }
    
    fclose(in);   /*Closes input file*/
    fclose(out);  /*Closes output file*/


    return 0;


}


int find_First_Letter (char **word_Array, int num_words){
    int i, word_index;
    char *First_Word;
    word_index = 0;
    
    for (i = 0; i < num_words; i++)   /*Find the first non-null pointer*/
    {
        if (word_Array[i] != NULL )
        {
            First_Word = word_Array[i];
            word_index = i;
            break;
        }
        
    }
    
    for (i = word_index + 1; i < num_words; i++)
    {
        if (word_Array[i] == NULL)   /*Null characters are to be ignored*/
        {
            continue;
        }
        else if (strcmp(First_Word, word_Array[i]) > 0)   /*Compare two strings to find if the current word is a higher value*/
        {
            First_Word = word_Array[i];
            word_index = i;
        }
        
    }
    
    return word_index; 
}

Could you kindly please explain what casting the result of malloc means?

I did what you mentioned but it is still not working. Sorry for causing you inconvenience.

@laserlight
When trying to compile these are the errors I am facing. Unsure of how to fix them.

In function ‘main’:
main.c:31:15: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
wordArray = (char*) malloc(num_words*sizeof(char)); /*Creates memory for every word*/
^
main.c:34:25: error: lvalue required as left operand of assignment
(wordArray + x) = (char*) malloc((num_letters + 1)*sizeof(char)); /*Creates memory for every letter in the word. +1 due to null character at the end*/
^
main.c:43:39: error: lvalue required as left operand of assignment
((wordArray + x) + y) = '\0'; /*Sets newline to a null character*/
^
main.c:45:39: error: lvalue required as left operand of assignment
((wordArray + x) + y) = c;
^
main.c:59:28: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
sortedwordArray[x] = wordArray[word_index];
^
main.c:61:5: error: expected ‘;’ before ‘}’ token
}
^
main.c:65:24: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
fprintf(out, "%s\n", sortedwordArray[x]); /*Output gets printed to the required file*/
^

Stop casting the return value of malloc, you are causing several errors with those casts.

Next what do you think (wordArray + x) is actually accomplishing?

Why aren't you using "normal" array notation instead of trying to confuse yourself by trying to use array notation?

Make sure all of your source lines are properly terminated.

Again stop casting the return value of malloc, doing so usually just hides problems.

I don't understand what you mean by me casting the return value of malloc.

Do you know what casting means and how it's done in C?

This contains a cast of the return value of malloc(): wordArray = (char*) malloc(10), note the highlight.

I understand what you are trying to get at but what exactly is my mistake? Please bear with me.

Well in several places you are casting the return value to the wrong type, for example a char instead of a char*. Since you use a cast the compiler is free to deduce that you know what you're doing and not report any issues with the cast. Remember casting is inherently dangerous and should be used with the upmost caution, and avoided whenever possible.

Originally Posted by Timmy10

I don't understand what you mean by me casting the return value of malloc.

Code:

   char *ptr = NULL;
   ptr = malloc(64);
   // NOT
   ptr = (char *) malloc(64);

malloc() returns a "void *" (Generic typeless pointer) which can be, and should be, assigned to a pointer of any data type without casting.

Originally Posted by jimblumberg

Well in several places you are casting the return value to the wrong type, for example a char instead of a char*. Since you use a cast the compiler is free to deduce that you know what you're doing and not report any issues with the cast. Remember casting is inherently dangerous and should be used with the upmost caution, and avoided whenever possible.

So I should never cast? Like is that a bad practice?

Originally Posted by Timmy10

So I should never cast? Like is that a bad practice?

Yes.

Code:

char *sortedwordArray = (char) malloc(num_words * sizeof(char));

sortedwordArray is a char *
malloc() returns a void *
You are casting a void * to a char (Not a pointer) then assigning to a char *!!! WRONG!!!

The following would have been legal but not recommended!

Code:

char *sortedwordArray = (char *) malloc(num_words * sizeof(char));

In almost all cases, please avoid casting a return from malloc()