Question

我有一个类，它通过将一个char *分成句子来返回一个char **。我可以分配内存并在某个时间点给它值，但是当我尝试返回它时，它完全没有了。

char **makeSentences(char *chapter, int *nSentences){
int num = *nSentences;
char* chap = chapter;
char **sentences;
sentences = (char**) malloc(sizeof(char*) * num);
int stops[num + 1];
stops[0] = 0;
int counter = 0;
int stop = 1;
while (chap[counter] != '\0'){
    if (chap[counter] == '.'){
        stops[stop] = counter + 1;
        printf("Place: %d\nStop Number: %d\n\n", counter, stop);
        stop++;
    }
    counter++;
}
for (int i = 0; i < num; i++){
    int length = stops[i+1] - stops[i];
    char characters[length+1];
    memcpy(characters, &chap[stops[i]], length);
    characters[length] = '\0';
    char *sentence = characters;
    sentences[i] = sentence;
    printf("%s\n",sentence);
    printf("%s\n", sentences[i]);
}
char* testChar = sentences[0];
printf("%s\n", sentences[0]);
printf("%s]n", testChar);
return sentences;
}

最后两行打印行不打印除换行符之外的任何内容，而完全相同的行（在for循环中）按预期打印。这是怎么回事？

Answer 1

问题在于这三行：

char characters[length+1];
char *sentence = characters;
sentences[i] = sentence;

在此处保存指向本地变量的指针。变量characters将在循环的每次迭代中超出范围，留下一个“数组”的杂散指针。

虽然在C中不是标准，但几乎所有系统都有strdup函数，通过调用malloc和strcpy来复制字符串。我建议你使用它（或实现你自己的）。

为什么指针消失了？

1 个答案: