Question

EDIT: I have changed my program according to suggestions people have made but I am unable to fix memory leaks. Also, I need to free them without using argc, so i need to somehow keep track of the array length so I marked the last element as null.

Currently I’m writing a C program that copies the command line arguments into a dynamically allocated array. My code looks like:

char **array;                                                                                                                                                                                     
int j;                                                                                                                                                                                        

array = malloc(sizeof(char*) * (argc + 1));                                                                                                                                                       
int i;                                                                                                                                                                                            
int index = 0;                                                                                                                                                                                    

for(i = 0; i < (argc); i++){                                                                                                                                                                      
    int length = strlen(*(argv + i));                                                                                                                                                             
    array[i] = malloc((length + 1) * sizeof(char));                                                                                                                                                                                                                                                                                                                                    
        // Cycle through all the chars and copy them in one by one                                                                                                                                
    for(j = 0; j <= length; j++){                                                                                                                                                                 
        array[i][j] = toupper(argv[i][j]);                                                                                                                                                        
    }                                                                                                                                                                                             
}      
array[i + 1] = NULL;                                                                                                                                                                                           

return array;      

Later, I try to free the memory:

char** array_copy = array;
while(*array_copy != NULL){
    free(*array_copy++);
}
free(*array_copy) // free the null at the end
free(array); 

However, I still get memory leaks. I’m not quite sure what I’m doing wrong. If anyone could give me tips that would be great.

Thank!

Answer 1

Your last line free(array) isn’t freeing your original malloc, because you’ve incremented array as you are freeing its contents.

Also (as others point out):

• your loop to free the array contents is checking for non-zero, but you don’t ensure that the elements are zero to begin with.

• You allocate argc+1 elements in array, when you only need argc.

• *(argv + i) is the same as argv[i].