c – 用随机数填充数组的程序中的内存错误

2023年12月17日 215次阅读

我有一个程序创建一个数组并用随机数填充它.然后,它会检查是否有重复项,并打印出每次重复发生的次数.一切正常,除了Memcheck告诉我有39个错误,我无法弄清楚导致它们的原因(我认为问题来自重复()方法)？

干杯,
掠夺

代码 –

#include <stdio.h>
#include <stdlib.h>
#include "random.h"

int main(void) {
    int array_size = 0;
    int *my_array;
    int i = 0;

    printf("Enter the size of the array:\n");
    scanf("%d", &array_size);

    my_array = malloc(array_size * sizeof my_array[0]);
    if (NULL == my_array) {
        fprintf(stderr, "memory allocation failed!\n");
        return EXIT_FAILURE;
    }

    for (i = 0; i < array_size; i++) {
        my_array[i] = rand() % array_size;
    }
    printf("What's in the array:\n");
    for (i = 0; i < array_size; i++) {
        printf("%d ", my_array[i]);
    }
    printf("\n");

    repeated(my_array, array_size);

    free(my_array);

    return EXIT_SUCCESS;
}

void repeated(int *my_array, int array_size) {
    int *array_tracker;
    int i;

    array_tracker = malloc(array_size * sizeof array_tracker[0]);

    for (i = 0; i < array_size; i++) {
        array_tracker[my_array[i]]++;
    }

    for (i = 0; i < array_size; i++) {
        if (array_tracker[i] > 1) {
            printf("%d occurs %d times\n", i, array_tracker[i]);
        }
    }

    free(array_tracker);
}

Memcheck输出 –

==23999== Memcheck, a memory error detector
==23999== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==23999== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==23999== Command: ./lab20c-prog
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x40091F: repeated (random.c:15)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x519148A: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Use of uninitialised value of size 8
==23999==    at 0x518DD8B: _itoa_word (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5192552: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x518DD95: _itoa_word (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5192552: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x5192669: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x5191536: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== Conditional jump or move depends on uninitialised value(s)
==23999==    at 0x51915B9: vfprintf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x5199718: printf (in /usr/lib64/libc-2.24.so)
==23999==    by 0x40092E: repeated (random.c:16)
==23999==    by 0x400799: main (random.c:42)
==23999== 
==23999== 
==23999== HEAP SUMMARY:
==23999==     in use at exit: 0 bytes in 0 blocks
==23999==   total heap usage: 4 allocs, 4 frees, 1,052,792 bytes allocated
==23999== 
==23999== All heap blocks were freed -- no leaks are possible
==23999== 
==23999== For counts of detected and suppressed errors, rerun with: -v
==23999== Use --track-origins=yes to see where uninitialised values come from
==23999== ERROR SUMMARY: 39 errors from 7 contexts (suppressed: 0 from 0)

最佳答案 您从未初始化array_tracker的内容.所以当你这样做时：

array_tracker[my_array[i]]++;

你正在增加一个未初始化的值.这就是为什么你对使用未初始化的值有很多抱怨.

您可以使用calloc()而不是malloc()来分配空间并将所有元素初始化为0.

array_tracker = calloc(array_size, sizeof array_tracker[0]);
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