將結構從x-> y轉換為xy並刪除malloc時出現Valgrind錯誤。 努力學習C（前16） - 額外學分

Question

我在學習C The Hard Way（ http://c.learncodethehardway.org/book/ex16.html ）的練習16中有額外學分的問題，我正在嘗試轉換結構，所以他們沒有使用malloc。 我提出了這個代碼（我不確定我是否應該粘貼原始代碼或鏈接就足夠了）：

#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;
}

代碼編譯沒有任何錯誤或警告，並按預期工作。 如果我通過Valgrind運行它，我得到以下輸出：

==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)

我無法理解Valgrind輸出，我將非常感謝任何解釋。 我試圖在Print_person函數中注釋掉這些行：

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

沒有他們Valgrind沒有發現任何錯誤，但我無法理解為什么。

Answer 1

您可以忽略此警告。 它與C標准庫中的正常（如果不常見）行為有關。

（具體來說， memchr()函數的Mac OS X實現，它在內存塊中搜索一個字節，通過一次讀取多個字節來優化內存訪問。這可能涉及訪問未初始化的內存超出了該塊，Valgrind將其檢測為潛在錯誤。）