将结构从 x->y 转换为 x.y 并删除 malloc 时出现 Valgrind 错误。艰难地学习 C（前 16）- 额外学分

Question

我在艰难地学习 C (http://c.learncodethehardway.org/book/ex16.html) 的练习 16 的额外学分部分有问题，我正在尝试转换结构，以便它们不使用 malloc。我想出了这段代码（我不确定我是否应该也粘贴原始代码或者 link 就足够了）：

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

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

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[])
{
    struct Person joe = {"Joe Alex", 32, 64, 140};
    struct Person frank = {"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);

    return 0;
}

代码编译没有任何错误或警告，并且按预期工作。如果我通过 Valgrind 运行它，我会得到以下输出：

==8556== Memcheck, a memory error detector
==8556== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==8556== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==8556== Command: ./ex16
==8556==
--8556-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option
--8556-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 2 times)
--8556-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 4 times)
Joe is at memory location 0x104802928:
Name: Joe Alex
==8556== Conditional jump or move depends on uninitialised value(s)
==8556==    at 0x1003FCC3F: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==8556==    by 0x1001F0BB6: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x1001FB005: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x1002209CE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x100220CA0: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x1001F6B91: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x1001F49F7: printf (in /usr/lib/system/libsystem_c.dylib)
==8556==    by 0x100000D58: Person_print (ex16.c:16)
==8556==    by 0x100000E34: main (ex16.c:28)
==8556==
    Age: 32
    Height: 64
    Weight: 140
Frank is at memory location 0x104802910:
Name: Frank Blank
    Age: 20
    Height: 72
    Weight: 180
Name: Joe Alex
    Age: 52
    Height: 62
    Weight: 180
Name: Frank Blank
    Age: 40
    Height: 72
    Weight: 200
==8556==
==8556== HEAP SUMMARY:
==8556==     in use at exit: 38,691 bytes in 425 blocks
==8556==   total heap usage: 504 allocs, 79 frees, 44,803 bytes allocated
==8556==
==8556== LEAK SUMMARY:
==8556==    definitely lost: 16 bytes in 1 blocks
==8556==    indirectly lost: 0 bytes in 0 blocks
==8556==      possibly lost: 13,130 bytes in 120 blocks
==8556==    still reachable: 25,545 bytes in 304 blocks
==8556==         suppressed: 0 bytes in 0 blocks
==8556== Rerun with --leak-check=full to see details of leaked memory
==8556==
==8556== For counts of detected and suppressed errors, rerun with: -v
==8556== Use --track-origins=yes to see where uninitialised values come from
==8556== ERROR SUMMARY: 12 errors from 1 contexts (suppressed: 0 from 0)

我无法理解此处的 Valgrind 输出，非常感谢任何解释。我试图在 Print_person 函数中注释掉那些行：

/* printf("\tAge: %d\n", who.age); */
/* printf("\tHeight: %d\n", who.height); */
/* printf("\tWeight: %d\n", who.weight); */

没有它们，Valgrind 没有发现任何错误，但我不明白为什么。

Answer 1

您可以忽略此警告。它与 C 标准库中的正常（如果异常）行为有关。

（具体来说，Mac OS X 实现 memchr() 函数，它在内存块中搜索一个字节，通过读取多个字节来优化内存访问一次。这可能涉及访问超出块末尾的未初始化内存，Valgrind 将其检测为潜在错误。）

将结构从 x->y 转换为 x.y 并删除 malloc 时出现 Valgrind 错误。艰难地学习 C（前 16）- 额外学分

Valgrind errors when converting structs from x->y to x.y and removing malloc. Learn C the hard way (ex 16) - extra credit

c

struct

valgrind