How to free char** array that allocated in calling function from main? - c

Question

this is the function that i am calling from main:
char** readTokens(char *userInput, const char *seperator)
{
char** c;
char line1[512],line2[512];
int wordCount = 0;
int index;
char* tmp;
strcpy(line1, userInput);
for (index=0;line1[index]!='\n';index++);
line1[index]='\0';
strcpy(line2,line1);
tmp = strtok(line1,seperator);
while (tmp!=NULL)
{
tmp=strtok(NULL,seperator);
wordCount = wordCount + 1;
}
if((wordCount) == ERROR)
{
return NULL;
}
c=(char**)malloc(((wordCount)+1)*sizeof(char*));
if (c == NULL)
{
printf("failed to allocate memory.\n");
return NULL;
}
tmp = strtok(line2,seperator);
index=0;
while (tmp!=NULL)
{
c[index]=(char*)malloc((strlen(tmp)+1*sizeof(char)));
if (c[index]==NULL)
{
printf("failed to allocate memory.\n");
return NULL;
}
strcpy(c[index],tmp);
tmp=strtok(NULL,seperator);
index++;
}
c[index] = NULL;//put NULL on last place
return c;
}
And this how i use it in main:
while (fgets(words, sizeof(words), filePointer) != NULL) // this line is a command of reading a line from the file.
{
/*here i am calling the function*/
array = readTokens(words, " ");
theGraph->graphEdges[index_i].sourceVertex = array[ZERO];
theGraph->graphEdges[index_i].destinationVertex = array[ONE];
theGraph->graphEdges[index_i].arcValue = atoi(array[TWO]);
for(index_j = ZERO ; index_j < vertexes ; index_j++)
{
if(theGraph->placeInTableIndex[index_j] == NULL)
{
theGraph->placeInTableIndex[index_j] = array[ZERO];
break;
}
else if(strcmp(theGraph->placeInTableIndex[index_j],array[ZERO]) == ZERO)
break;
}
for(index_j = ZERO ; index_j < vertexes ; index_j++)
{
if(theGraph->placeInTableIndex[index_j] == NULL)
{
theGraph->placeInTableIndex[index_j] = array[ONE];
break;
}
else if(strcmp(theGraph->placeInTableIndex[index_j],array[ONE]) == ZERO)
break;
}
theGraph->graphEdges[index_i+ONE].sourceVertex = array[ONE];
theGraph->graphEdges[index_i+ONE].destinationVertex = array[ZERO];
theGraph->graphEdges[index_i+ONE].arcValue = atoi(array[TWO]);
index_i+= TWO;
//freeTokens(array);
}
I tried to do free to the array in the end of the while but it not work i still have memory leak from this function (valgrind check). i am using this function to free:
void freeTokens(char** tokens)
{
while(*tokens != NULL)
{
*tokens = NULL;
free(*tokens);
*tokens++;
}
tokens = NULL;
free(tokens);
}

Answer 1

You're losing the original value of tokens (the thing you need to free) by incrementing it; then you set it to NULL, then try to free NULL.
Instead:
void freeTokens(char** tokens)
{
char **freeTokens = tokens;
while (*freeTokens != NULL)
{
free(*freeTokens);
*freeTokens = NULL; // not actually necessary, but must happen *after* if at all
freeTokens++;
}
free(tokens);
// tokens = NULL; // accomplishes nothing; doesn't change the caller's version
}