valgrind如何计算我的示例内存泄漏？

我有意删除结构的释放，并想了解valgrind如何计算内存泄漏。valgrind如何计算我的示例内存泄漏？

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

struct Person{ 
    char *name; 
    int age; 
    int height; 
    int weight; 
}; 

struct Person *Person_create(char *name, int age, int height, int weight){ 
    struct Person *who = malloc(sizeof(struct Person)); 
    assert(who != NULL); 

    who->name = strdup(name); 
    who->age = age; 
    who->height = height; 
    who->weight = weight; 

    return who; 
} 

void Person_destroy(struct Person *who){ 
    assert(who != NULL); 
    free(who->name); 
    free(who); 
} 

void Person_print(struct Person *who){ 
    printf("Name: %s\n", who->name); 
    printf("\tAge: %d\n", who->age); 
    printf("\tHeight: %d\n", who->height); 
    printf("\tWeight: %d\n", who->weight); 
} 

int main(int argc, char *argv[]){ 
    //make two people structures 
    struct Person *joe = Person_create("Joe Alex", 32, 64, 140); 
    struct Person *frank = Person_create("Frank Blank", 20, 72, 180); 

    //print them out and where they are in memory 
    printf("Joe is at memory location %p\n", joe); 
    Person_print(joe); 

    printf("Frank is at memory location %p\n", frank); 
    Person_print(frank); 

    //make everyone age 20 years and print them again 
    joe->age += 20; 
    joe->height -= 2; 
    joe->weight += 40; 
    Person_print(joe); 

    frank->age += 20; 
    frank->weight += 20; 
    Person_print(frank); 

// Person_destroy(joe); 
// Person_destroy(frank); 

    return 0; 
}

Valgrind的输出：

==7687== HEAP SUMMARY: 
==7687==  in use at exit: 69 bytes in 4 blocks 
==7687== total heap usage: 4 allocs, 0 frees, 69 bytes allocated 
==7687== 
==7687== 33 (24 direct, 9 indirect) bytes in 1 blocks are definitely lost in loss record 3 of 4 
==7687== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) 
==7687== by 0x40067B: Person_create (ex16.c:14) 
==7687== by 0x4007B9: main (ex16.c:40) 
==7687== 
==7687== 36 (24 direct, 12 indirect) bytes in 1 blocks are definitely lost in loss record 4 of 4 
==7687== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) 
==7687== by 0x40067B: Person_create (ex16.c:14) 
==7687== by 0x4007D6: main (ex16.c:41) 
==7687== 
==7687== LEAK SUMMARY: 
==7687== definitely lost: 48 bytes in 2 blocks 
==7687== indirectly lost: 21 bytes in 2 blocks 
==7687==  possibly lost: 0 bytes in 0 blocks 
==7687== still reachable: 0 bytes in 0 blocks 
==7687==   suppressed: 0 bytes in 0 blocks 
==7687== 
==7687== For counts of detected and suppressed errors, rerun with: -v 
==7687== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

如果我不免费2个结构创建，泄漏应为4 * 4 * 2 = 32个字节。为什么字节总数泄漏48？

从uname - -a

平台信息： Linux的mymachine上3.13.0-43泛型＃72，Ubuntu的SMP周一12月8日19时35分06秒UTC 2014 x86_64的x86_64的x86_64的GNU/Linux的

来源

2014-12-21 drdot

您编译支持64位平台与32位整数，而结构是越来越布局如下：

char *name; /* 8 bytes */ 
int age;  /* 4 bytes */ 
int height; /* 4 bytes */ 
int weight; /* 4 bytes */ 
      /* 4 bytes of padding to make it possible to create */ 
      /* correctly-aligned arrays of struct Person  */

因此sizeof(struct Person)是24，而不是作为16你承担。其中两个使48字节。

有关填充和对齐的讨论，请参见Why isn't sizeof for a struct equal to the sum of sizeof of each member?

来源

2014-12-21 20:01:55 NPE

感谢您的提醒。我在更新中指定了它。 – drdot

@dannycrane：然后指针肯定是64位宽，并且在结构的末尾有填充。查看更新后的答案。 – NPE

为什么最后需要填充？ – drdot

当你问M字节，库分配M + x字节，其中'x'是它需要跟踪的数字。这些可能是一个标题，可能会将存储量增加到某个标准块。

来源

2014-12-21 19:58:32 bmargulies

valgrind如何计算我的示例内存泄漏？

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