Thread: Program Crashing - Possibly Related to Dynamic Memory Allocation

I wrote a program that tries to store the whole content of a file (its own source code) in a pointer to char variable, and then tries to print that content when the EOF is reached in the file. The program is crashing so far. I added the following line to it, so that I can clearly see the character just read:

printf( "***%c***\n", currentCharacter );

The program compiles and links properly, but the output ends up being:



The program is:

Code:

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

int stringLength( char *arr );

int main( void )
{
    int counter = 0;
    
    char *charPtr = NULL;
    
    char currentCharacter;
    
    FILE *filePtr = fopen( "read_content_to_array.c", "r" );
    
    if ( filePtr != NULL )
    {
        while ( !feof( filePtr ) )
        {
            currentCharacter = fgetc( filePtr );
            
            printf( "***%c***\n", currentCharacter );
            
            if ( counter > 0 )
            {
                if ( ( charPtr = realloc( charPtr, ( 1 + stringLength( charPtr ) ) * sizeof( char ) ) ) != NULL )
                {
                    *( charPtr + counter ) = currentCharacter;
                    *( charPtr + counter + 1 ) = '\0';
                }
                else
                {
                    printf( "Memory error...\n" );
        
                    return 1; 
                }
            }
            else
            {
                if ( ( charPtr = malloc( 2 * sizeof( char ) ) ) != NULL )
                {
                    *( charPtr + counter ) = currentCharacter;
                    *( charPtr + counter + 1 ) = '\0';
                }
                else
                {
                    printf( "Memory error...\n" );
        
                    return 1; 
                }
            }
            
            ++counter;
        }
        
        if ( counter > 0 )
        {
            printf( "%s", charPtr );
    
            free( charPtr );
        }

        fclose( filePtr );
    }
    else
    {
        printf( "File error...\n" );
        
        return 1;
    }
    
    return 0;
}

int stringLength( char *arr )
{
    int i = 0;
    int length = 0;
    
    while ( *( arr + i++ ) != '\0' )
    {
        ++length;
    }
    
    return length;
}

What am I doing wrong? Thanks in advance.

[EDIT:] I tried using two pointer variables, as suggested to telmo_d in the last answer of the topic located in How to get address of the start of the memory allocated?, but the program still crashes. Here's the modified program:

Code:

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

int stringLength( char *arr );

int main( void )
{
    int counter = 0;
    
    char *charPtr1;
    char *charPtr2;
    
    char currentCharacter;
    
    FILE *filePtr = fopen( "read_content_to_array.c", "r" );
    
    if ( filePtr != NULL )
    {
        while ( !feof( filePtr ) )
        {
            currentCharacter = fgetc( filePtr );
            
            printf( "***%c***\n", currentCharacter );
            
            if ( counter > 0 )
            {
                if ( ( charPtr2 = realloc( charPtr1, ( 1 + stringLength( charPtr1 ) ) * sizeof( char ) ) ) != NULL )
                {
                    charPtr1 = charPtr2;
                    
                    *( charPtr1 + counter ) = currentCharacter;
                    *( charPtr1 + counter + 1 ) = '\0';
                }
                else
                {
                    printf( "Memory error...\n" );
        
                    return 1; 
                }
            }
            else
            {
                if ( ( charPtr1 = malloc( 2 * sizeof( char ) ) ) != NULL )
                {
                    *( charPtr1 + counter ) = currentCharacter;
                    *( charPtr1 + counter + 1 ) = '\0';
                }
                else
                {
                    printf( "Memory error...\n" );
        
                    return 1; 
                }
            }
            
            ++counter;
        }
        
        if ( counter > 0 )
        {
            printf( "%s", charPtr1 );
    
            free( charPtr1 );
            free( charPtr2 );
        }

        fclose( filePtr );
    }
    else
    {
        printf( "File error...\n" );
        
        return 1;
    }
    
    return 0;
}

int stringLength( char *arr )
{
    int i = 0;
    int length = 0;
    
    while ( *( arr + i++ ) != '\0' )
    {
        ++length;
    }
    
    return length;
}

You seem to be trying to free your malloc() memory twice. You only allocate memory for charPtr2 but you try to free both charPtr1 and charPtr2.

Jim

It's high time you read this FAQ and paid attention to it!
FAQ > Why it's bad to use feof() to control a loop - Cprogramming.com

Code:

                if ( ( charPtr2 = realloc( charPtr1, ( 1 + stringLength( charPtr1 ) ) * sizeof( char ) ) ) != NULL )
                {
                    charPtr1 = charPtr2;
                     
                    *( charPtr1 + counter ) = currentCharacter;
                    *( charPtr1 + counter + 1 ) = '\0';
                }

charPtr2 is only ever a temporary variable to make sure the realloc worked, before updating charPtr1.

> 1 + stringLength( charPtr1 )
Think carefully about what this is, and what you need when storing your data.

You might also want to think about the overall efficiency of calling stringLength() every single time when the string just gets longer and longer.
Compare the result of stringLength() with counter


FWIW, you need to use better variable names.