c - 字符串末尾的随机字符

Question

我在 C 语言(使用 GCC)中创建了一个加密字符串的函数，但我在解密字符串的末尾得到了随机字符。该函数将在第一个字符处保存输入字符串的长度，在第二个字符处保存使用的键(第一个字符 -1)。所有要加密的字符串的长度都在 10 到 30 之间，所以我希望在转换为存储为 char 时没有问题。

完整代码在这里:

#include <stdio.h> //printf
#include <stdlib.h> //malloc
#include <string.h> //strlen

char* x(const char* toEncrypt);
char* y(const char* toDecrypt);

int main() {
    const char *secret = "hellohello";
    printf("original: %s\n", secret);

    const char* crypted = x(secret);
    printf("crypted: %s\n", crypted);

    const char* decrypted = y(crypted);
    printf("decrypted: %s\n", decrypted);

    return 0;
}

char* x(const char* toEncrypt) {
    printf("x->toEncrypt = %s\n", toEncrypt);

    int offset = 0, i = 0;
    int length = strlen(toEncrypt);
    printf("\tx->length = %d\n", length);

    char key = ((char)(*toEncrypt))-1;
    printf("\tx->key = %c\n", key);

    char* output = (char*)malloc(length+3); //toEncrypt length + (length + key + null)

    output[offset++] = (char)length;
    output[offset++] = key;

    for (i = 0; i < length; i++) {
        printf("i = %d\toffset = %d\tchar = %c\n", i, offset, toEncrypt[i]);
        output[offset++] = toEncrypt[i] ^ key;
    }
    output[offset] = '\0';

    printf("\tx->output = %s\n", output);
    return output;
}

char* y(const char* toDecrypt) {
    printf("y->toDecrypt = %s\n", toDecrypt);

    int offset = 0, i = 0;
    int length = (int)toDecrypt[offset++] ;
    printf("\tx->length = %d\n", length);

    char key = (char)toDecrypt[offset++];
    printf("\ty->key = %c\n", key);

    char* output = (char*)malloc(length+1);

    for (i = 0; i < length; i++) {
        printf("i = %d\toffset = %d\tchar = %c\n", i, offset, (char)toDecrypt[offset] ^key);
        output[i] = toDecrypt[offset++] ^ key;
    }

    output[offset] = '\0';

    printf("\ty->output = %s\n", output);
    return output;
}

输出:

original: hellohello
x->toEncrypt = hellohello
        x->length = 10
        x->key = g
i = 0   offset = 2      char = h
i = 1   offset = 3      char = e
i = 2   offset = 4      char = l
i = 3   offset = 5      char = l
i = 4   offset = 6      char = o
i = 5   offset = 7      char = h
i = 6   offset = 8      char = e
i = 7   offset = 9      char = l
i = 8   offset = 10     char = l
i = 9   offset = 11     char = o
        x->output =
g
crypted:
g
y->toDecrypt =
g
        x->length = 10
        y->key = g
i = 0   offset = 2      char = h
i = 1   offset = 3      char = e
i = 2   offset = 4      char = l
i = 3   offset = 5      char = l
i = 4   offset = 6      char = o
i = 5   offset = 7      char = h
i = 6   offset = 8      char = e
i = 7   offset = 9      char = l
i = 8   offset = 10     char = l
i = 9   offset = 11     char = o
        y->output = hellohellobe
decrypted: hellohellobe

Answer 1

我认为问题在于这个语句(在函数 y() 中 — 在函数 x() 中的相同语句是可以的):

output[offset] = '\0';

应该是:

output[i] = '\0';

更改此设置应该有效。