|C/C++| find memory leak, Valgrind

This article will introduce an well-known tool for detecting the memory leak,

Valgrind

Install in Ubuntu:

sudo apt-get install valgrind

Test code, check_leak_demo.c

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

struct leak_example {
    char *ptr;
};

void leak1(void){
    int *ptr = (int *)malloc(100);
    if (!ptr) {
        printf("Oops, malloc fail!\n");
    }
}

char *leak2(void){
    char *ptr = strdup("Hey Hey Hey!\n");
    if (!ptr) {
        printf("Oops, strdup fail!\n");
        return 0;
    }
    return ptr;
}

struct leak_example *leak3(void){
    struct leak_example *ptr = 0;
    ptr = (struct leak_example *) malloc(sizeof(struct leak_example));
    if (!ptr) {
        printf("Oops, malloc fail!\n");
    }
    ptr->ptr = strdup("Hey Hey Hey!\n");
    return ptr;
}

int main(){
    struct leak_example *lk_ptr;
    char * ch_ptr = 0;
    leak1();
    ch_ptr = leak2();
    if(ch_ptr) {
        printf("%s", ch_ptr);
    }
    lk_ptr = leak3();
    if(lk_ptr) {
        printf("%s", lk_ptr->ptr);
        free(lk_ptr);
    }
    return 0;
}

Build command

$ gcc -g -o check_leak_demo check_leak_demo.c

Execute Valgrind

$ valgrind --leak-check=full --show-leak-kinds=all --verbose ./check_leak_demo

Test result:

// there are 3 leaks


How to modify leak ?
check my comments “//solve leak“.

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

struct leak_example {
    char *ptr;
};

void leak1(void){
    int *ptr = (int *)malloc(100);

    if (!ptr) {
        printf("Oops, malloc fail!\n");
    }
    free(ptr); //solve leak
}

char *leak2(void){
/* //method 2
    char test[20];
    sprintf( test, "Hey Hey Hey!\n");
    return strdup(test);
*/
    char *test = "Hey Hey Hey!\n";
    char *ptr = strdup(test);

    if (!ptr) {
        printf("Oops, strdup fail!\n");
        return 0;
    }
    return ptr;
}

struct leak_example *leak3(void){
    struct leak_example *l_ptr = 0;
    l_ptr = (struct leak_example *) malloc(sizeof(struct leak_example));
    if (!l_ptr) {
        printf("Oops, malloc fail!\n");
    }
    l_ptr->ptr = strdup("Hey Hey Hey!\n");
    return l_ptr;
}

int main(){
    struct leak_example *lk_ptr;
    char * ch_ptr = 0;
    leak1();
    ch_ptr = leak2();
    if(ch_ptr) {
        printf("%s", ch_ptr);
        free(ch_ptr);//solve leak
    }
    lk_ptr = leak3();
    if(lk_ptr) {
        printf("%s", lk_ptr->ptr);
        free(lk_ptr->ptr);//solve leak
        free(lk_ptr);
    }
    return 0;
}

Reference:
http://wen00072.github.io/blog/2014/11/29/catching-leakage-use-valgrind-checking-c-memory-leak/