Thread: Can't free

I'm working on an assignment that handles text and operations on the text. What I have so far is

Code:

//tests.c
//Compile: gcc -Wall -Werror -O -o text textbuffer.c tests.c

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

#include "textbuffer.h"

void initialize (void);

int main (int argc, char *argv[]) {
    initialize ();
    return EXIT_SUCCESS;
}

void initialize (void) {
    {
        TB TestSubject;
        printf("\nTest 1: Initialize with text \"abcd\"\n");   
        TestSubject = newTB("abcd");
        printf("Print text -\n%s\n", dumpTB(TestSubject));
        printf("Free text buffer\n");
        releaseTB(TestSubject);
        printf("Passed\n\n");
    }
    
    {
        TB TestSubject;
        printf("Test 2: Text = \"u\\nda\\nsexay \\nno homo\"\n");   
        TestSubject = newTB("u\nda\nsexay \nno homo");
        printf("Print text - \n%s\n", dumpTB(TestSubject));
        printf("Number of lines = %d\n", linesTB(TestSubject));
        printf("Free text buffer\n");
        releaseTB(TestSubject);
        printf("Attempt to find numLines should result in error:\n");
        printf("%d\n", linesTB(TestSubject));
        printf("Passed\n\n");
    }
    
    return;
}

Code:

//textbuffer.c

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

#include "textbuffer.h"

typedef struct textbuffer *TB;
struct textbuffer {
    char *text;
	int numLines;
};

/* Allocate a new textbuffer whose contents is initialised with the text given
 * in the array.
 */
TB newTB (char text[]) {
	TB Buff = malloc(sizeof(struct textbuffer));
	assert (Buff != NULL);
	
	int lineCount = 1;
	int length = strlen(text);
	int i;
	
	for (i=0; i<length; i++) {
	    if (text[i] == '\n')
	        lineCount++;
	}
	Buff->numLines = lineCount;
	
	Buff->text = malloc(sizeof(char)*strlen(text));
	strcpy(Buff->text, text);
	
	return Buff;
}


/* Free the memory occupied by the given textbuffer.  It is an error to access
 * the buffer afterwards.
 */
void releaseTB (TB tb) {
    free(tb->text);
    free(tb);
}

/* Allocate and return an array containing the text in the given textbuffer.
 */
char *dumpTB (TB tb) {
    return tb->text;
}


/* Return the number of lines of the given textbuffer.
 */
int linesTB (TB tb) {
    return tb->numLines;
}

With a header file for the function declarations.

My problem is that I can't seem to free the text and struct itself because when I call releaseTB which is supposed to free, I can still access the struct with no problem.

I suppose that depends on what you mean by "error" -- line 38 (in your main program) is an error, but a logic error, not a runtime error. The memory referenced by that pointer still exists, and if you're quick about it the memory might not have gotten reused yet, but there will always be some sort of data there, just maybe not your data.

(EDIT: Hence good practice if you don't trust yourself or your other programmers is to set the pointer to NULL after you free it, which will cause a runtime error when you try to dereference it.)

Ok cheers for that