Valgrind Error in C ,,Conditional jump or move depends on uninitialised value(s)''/ even though they are initialized

Question

//#include "rand_malloc.h"
#include <stdio.h>
#include <stdlib.h>
#define SPACE 32
#define ENTER 13
#define STOP 10

int shouldRead = 1;
char** text;
char* newline;
char* crln;
int text_size = 1;

void clearMemory()
{
    for (int i = 0; i < text_size - 1; i++) {
        free(text[i]);
        text[i] = NULL;
    }
    free(text);
}

void clearMemoryError()
{
    for (int i = 0; i < text_size - 1; i++) {
        free(text[i]);
        text[i] = NULL;
    }
    free(text);
    free(crln);
    exit(0);
}

void checkSinglePointer(char* ptr, char* error)
{
    if (ptr == NULL) {
        printf("%s\n", error);
        clearMemoryError();
    }
}

void checkDoublePointer(char** ptr, char* error)
{
    if (ptr == NULL) {
        printf("%s\n", error);
        clearMemoryError();
    }
}

char* readline()
{
    char* tm = NULL;
    char c;
    int size = 1;
    crln = malloc((size) * sizeof(char));
    while ((c = getchar()) != STOP) {
        if (c == EOF) {
            free(crln);
            return NULL;
        }
        crln[size - 1] = c;
        size++;
        tm = realloc(crln, (size) * sizeof(char));
        checkSinglePointer(tm, "E");
        crln = tm;
    }
    size++;
    tm = realloc(crln, (size) * sizeof(char));
    checkSinglePointer(tm, "E");
    crln = tm;
    crln[size - 1] = '\n';
    return crln;
}

int main(int argc, char* argv[])
{
    char** tm = NULL;
    text = malloc(text_size * sizeof(char*));
    checkDoublePointer(text, "E");
    while (shouldRead) {
        newline = readline();
        if (newline == NULL) {
            break;
        }
        text[text_size - 1] = newline;
        printf("%p", newline);
        printf("%s", text[0]);
        text_size++;
        tm = realloc(text, text_size * sizeof(char*));
        checkDoublePointer(tm, "E");
        text = tm;
    }
    clearMemory();
    return 0;
}

Hi, I am trying to write a programm that as input takes text and then reverse it. I am checking for memory leaks using valgrind, everything is fine but when I am trying to e.x

printf("%s", text[0]); // Any other index also doesn't work.

I am getting error ,,Conditional jump or move depends on uninitialised value(s)" even though it contains text which is printed.

Answer 1

When printing a string, printf will need a string-terminator '\0'. However, not finding it would cause a Valgrind error, since you are easily able to go out of your malloc-ed string. A fix to that would be to use calloc, like so:

char *str = calloc(sizeof(char), STRING_SIZE + 1);

Which is equivalent to doing this:

char *str = malloc(sizeof(char) * STRING_SIZE + 1);
str = memset(str, 0, STRING_SIZE + 1);

Your whole string will be filled with string-terminator characters, which I would recommend to always do when allocating anything, to avoid unexpected behaviour.

Also, don't forget to check if malloc or calloc returns NULL: it's good practice.