When should I use free() in C?

Asked 2011-09-13T04:46:29.577

The code works as it is supposed to, though it never frees the memory allocated by malloc().

I have tried to free memory in any place that I can, but no matter where I do it, it breaks the program. Specifically, I get a "double free or corruption error." This is more of a question as to what free() and malloc() actually do? All of the problems with free are in the main:

int main(int argc,  char *argv[]){
if(argc!=2){
    exit(1);
}

printf("CSA WC version 1.0\n\n");

int length = strlen(argv[argc-1]);
char file_to_open[length];
strcpy(file_to_open, argv[argc-1]);

//printf("filename:%s\n",file_to_open);

//create counters for output
int count_number_of_lines = 0;
int count_number_of_words = 0;
int count_number_of_characters = 0;

//create int size of default array size
int current_array_size = pre_read(file_to_open);
//printf("number of lines: %i\n",current_array_size);

//create string array of default size
char *strings_array[current_array_size];

//create a pointer to catch incoming strings
char *incoming_string=NULL;

int done=0;
while(done==0){
    incoming_string=get_line_from_file(file_to_open, count_number_of_lines);
    if(incoming_string!=NULL){
        incoming_string=csestrcpy2(incoming_string);
        //printf("incoming line: %s\n",incoming_string);
        strings_array[count_number_of_lines]=(char*)malloc(strlen(incoming_string+1));
        strings_array[count_number_of_lines]=csestrcpy2(incoming_string);
        //printf("added to array:%s\n",strings_array[count_number_of_lines]);
        count_number_of_lines++;
        count_number_of_characters=(count_number_of_characters+(strlen(incoming_string)-1));
    }
    else{
        done=1;
    }

}
//all data is stored in a properly sized array


//count all words in array
int count=0;
int word_count=0;
char *readline;

while(count<current_array_size){
    readline = csestrcpy2(strings_array[count]);
    printf("line being checked: %s"



        
            2 Answers
            
            
                
                    
                        
                            
                            
                        
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                        Dynamic memory allocation (malloc) allocates a memory block of requested size, and returns a pointer to the start of this block.Since we have taken this block from memory so its a good practice to return this back to memory after completion of task.

Now as answer of your question , To be always on safe side you can call free function before making return.

main{
    int *i;
    ..
    ..
    i=(int *)malloc(sizeof(int));
    ...//so something with i
    ..
    free(i);
    return 0;
}


                        
                        
                            answered 2013-05-01T13:13:34.923
                            
                        
                        
                            
                                
                                
                            
                        
                        
                            
                            
                            
                                
                                
                            
                            
                        
                    
                
            
            
            
                
                    
                        
                            
                            
                        
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                        As a general rule, for every malloc there should be a corresponding free.  You cannot however free something twice (as you have noticed by now).  I don't see any calls to free in your code, so it's impossible to say where your problem lies, but I noticed right away that you malloc some memory and assign it to readline inside of a loop, yet you don't call free on readline at the end of the loop, so you are leaking memory there.

                        
                        
                            answered 2011-09-13T04:56:35.450
                            
                        
                        
                            
                                
                                
                            
                        
                        
                            
                            
                            
                                
                                
                            
                            
                        
                    
                
            
            
        

        
        
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