如果malloc不回傳任何內容，如何停止for回圈和程式

所以我有這個 for 回圈，我為指標陣列中的每個字串分配記憶體

for (int i = 0; i < N;   i) {
    ptr[i] = malloc(14 * sizeof(char));
}

如果我檢查回圈本身的malloc回傳值for，我的學校編譯器會給我一些錯誤

    for (int i = 0; i < N;   i) {
        ptr[i] = malloc(14 * sizeof(char));
        if (!ptr[i]) {
            fprintf(stderr, "Out of memory!\n");
            exit(-10);
        } 
    }

如何malloc在for回圈中正確檢查回傳值和記憶體是否實際分配？

代碼：

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

#define N  2

int main(void) {
    char **ptr;
    ptr = (char **)malloc(N * (sizeof(char *)));
    if (!ptr) {
        fprintf(stderr, "Out of memory!\n");
        exit(-10);
    }
    char *hamburger = "hamburger";
    char *icecream = "icecream";

    for (int i = 0; i < N;   i) {
        ptr[i] = malloc(10 * sizeof(char));
        if (!ptr[i]) {
            fprintf(stderr, "Out of memory!\n");
            exit(-10);
        }
    }

    strcpy(ptr[0], hamburger);
    strcpy(ptr[1], icecream);
    char *end = "pay";
    char input[80] = "";
    int price = 0;
    while (!str_compare(input, end)) {
        scanf("%s", input);
        if (str_compare(ptr[0], input))
            price  = 150;
        if (str_compare(ptr[1], input))
            price  = 40;
    }
    printf("Total price %d", price);

    for (int i = 0; i < N; i  ) {
        free(ptr[i]);
    }

    free(ptr);
    ptr = NULL;
    hamburger = NULL;
    icecream = NULL;
 
    end = NULL;
    return 0;
}

錯誤：D

================================================== ==================13==錯誤：AddressSanitizer：堆緩沖區溢位在地址 0x6020000000dd 上 pc 0x5637075280da bp 0x7ffc25536920 sp 0x7ffc255360c8 WRITE 00050000000080000000000008000000008000000000000000000000800800080007在 __interceptor_strcpy.part.0 (/work/main 0x380d9) #1 0x5637075c8836 在 main FINAL-FASTFOOD.c:69 #2 0x7fc505e0bcb1 在 __libc_start_main (/lib/x86_6c1bc.0x86_64-bcb1) 3 0x5637074f843d 在 _start (/work/main 0x843d)

0x6020000000dd is located 0 bytes to the right of 13-byte region [0x6020000000d0,0x6020000000dd) allocated by thread T0 here: #0 0x563707584d77 in malloc (/work/main 0x94d77) #1 0x5637075c85a7 in main FINAL-FASTFOOD.c:53 #2 0x7fc505e0bcb1 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6 0x28cb1)

SUMMARY: AddressSanitizer: heap-buffer-overflow (/work/main 0x380d9) in __interceptor_strcpy.part.0 Shadow bytes around the buggy address: 0x0c047fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c047fff8000: fa fa 00 05 fa fa 00 05 fa fa 00 05 fa fa 00 05 =>0x0c047fff8010: fa fa 00 05 fa fa 00 05 fa fa 00[05]fa fa fa fa 0x0c047fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c047fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Freed heap region: fd
Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order:
f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal:
fe Left alloca redzone: ca Right alloca redzone: cb
Shadow gap: cc ==13==ABORTING

uj5u.com熱心網友回復：

問題中的代碼與程式中的代碼不一致：您使用了14位元組的長度 vs：程式中的10個位元組...您確定發布的代碼會發生錯誤嗎？

執行的分配看起來是正確的，但是當您在實際讀取輸入之前比較輸入時，比較回圈是不正確的。此外，您沒有告知scanf()要存盤的最大位元組數input，這可能會導致長輸入字的未定義行為：這是攻擊者可以用來嘗試執行任意代碼的典型缺陷。

這是一個修改后的版本：

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

#define N  2

bool str_compare(const char *s1, const char *s2) {
    return !strcmp(s1, s2);
}

int main(void) {
    char **ptr;
    ptr = malloc(N * (sizeof(char *)));
    if (!ptr) {
        fprintf(stderr, "Out of memory!\n");
        exit(-10);
    }
    const char *hamburger = "hamburger";
    const char *icecream = "icecream";

    for (int i = 0; i < N;   i) {
        ptr[i] = malloc(10 * sizeof(char));
        if (!ptr[i]) {
            fprintf(stderr, "Out of memory!\n");
            exit(-10);
        }
    }

    strcpy(ptr[0], hamburger);
    strcpy(ptr[1], icecream);

    const char *end = "pay";
    char input[80];
    int price = 0;
    while (scanf("ys", input) == 1 && !str_compare(input, end)) {
        if (str_compare(ptr[0], input))
            price  = 150;
        else
        if (str_compare(ptr[1], input))
            price  = 40;
        else
            printf("unknown item: %s\n", input);
    }
    printf("Total price %d\n", price);

    for (int i = 0; i < N; i  ) {
        free(ptr[i]);
    }
    free(ptr);

    return 0;
}

uj5u.com熱心網友回復：

您正在分配 2 *char指標，但for回圈分配了 3 次。上次分配記憶體的時候啊緩沖區溢位發生了，因為你沒有分配3*char指標

嘗試for像這樣改變回圈：

For(int i=0; i <= N; i  )

標籤：c malloc

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