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无法正确访问Struct内容

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我没有得到以下字符串输出：

struct stringItem {
    int len;
    char str[1];
} 

 void allocationStringBuffer (char* stringContent, struct stringItem *string) {

    // dynamically sized object
    int n;
    n = strlen(stringContent);

    //struct stringItem *string = malloc(sizeof(struct stringItem) + n);
    string = malloc(sizeof(struct stringItem) + n);

    if (string == NULL) {             // check if malloc is successful
       printf("Memory allocation for string fails.\n");
       // exit(-1);
    }   

   strcpy(string->str, stringContent);
   printf("Struct string: %s\n", string->str);
   string->len = n;     
}
 

 in main: 

 struct stringItem *string2;

allocationStringBuffer ("helloWorld", string2);

printf("Struct string: %s\n", (*string2).str);
free(string2);

allocationStringBuffer ("another Statement...", string2);
printf("Struct string: %s\n", string2->str);
free(string2);
 

 The result is: 

 Struct string: helloWorld
Struct string:  ÉÉÉÉÉï Uï∞â∞¶SVWh♦☺
Struct string: another Statement...
Struct string:  ÉÉÉÉÉï Uï∞â∞¶SVWh♦☺
 

 Thank you for your help. 

 [Updates with Thanks to ALL]
Here is the full working code. It has been resolved. Thank you to ALL.

struct stringItem {
    int len;
    char str[1];
};


void allocationStringBuffer (char* stringContent, struct stringItem** pstring) {

    // dynamically sized object
    int n;
    n = strlen(stringContent);

    struct stringItem *string;
    string = malloc(sizeof(struct stringItem) + (n+1));

    if (string == NULL) {             // check if malloc is successful
       printf("Memory allocation for string fails.\n");
       // exit(-1);
    }   

   strcpy(string->str, stringContent);
   printf("Struct string: %s\n", string->str);
   string->len = n;     

   *pstring = string;  // Copy allocated pointer to out-parameter.
}


 

 in main 

    

struct stringItem *string2;

allocationStringBuffer ("helloWorld", &string2);

printf("Struct string: %s\n", (*string2).str);
free(string2);

allocationStringBuffer ("another Statement...", &string2);
printf("Struct string: %s\n", string2->str);
free(string2);
c struct parameter-passing

4 回答

  • 0

    在我看来，你需要做出这些改变：

    allocationStringBuffer ("helloWorld", &string2);  // Pass ADDRESS of string2, not just string2

    void allocationStringBuffer (char* stringContent, struct stringItem **pstring)
{
    // dynamically sized object
    int n;
    n = strlen(stringContent);

    struct stringItem* string;  // Local variable, will be later copied to function parameter.
    string = malloc(sizeof(struct stringItem) + n);

    if (string == NULL) {             // check if malloc is successful
       printf("Memory allocation for string fails.\n");
       // exit(-1);
    }   

   strcpy(string->str, stringContent);
   printf("Struct string: %s\n", string->str);
   string->len = n;     

   *pstring = string;  // Copy allocated pointer to out-parameter.
}
    回复于
  • 0

    这个似乎不对：

    string = malloc(sizeof(struct stringItem) + n);

    你想在这做什么？ string 是 struct stringItem 的元素 . 所以我认为你只需要分配 string = malloc(sizeof(struct stringItem));

    p / s：如果你发布struct stringItem的声明，我应该很好

    回复于
  • 3

    您缺少 malloc 调用中的终止空字符 .

    string = malloc(sizeof(struct stringItem) + (n + 1));

    strlen 为您提供不包括终止空字符的大小 .

    问候，

    回复于
  • 0

    你将一个指向stringItem的指针传递给函数，然后用 malloc 返回覆盖参数，然后丢弃它，从而泄漏它的内存 . 您有两种方法可以解决此问题：

    void allocationStringBuffer(char* stringContent, struct stringItem** string) {
    int length = strlen(stringContent);
    *string = malloc(sizeof(struct stringItem) + length + 1);
    /* The +1 is padding.  You do want that. */
    strcpy(*string->str, stringContent);
}

    要么：

    struct stringItem* allocationStringBuffer(char* stringContent) {
    int length = strlen(stringContent);
    struct stringItem* string = malloc(sizeof(struct stringItem) + length + 1);
    strcpy(string->str, stringContent);
    return string;
}

    基本上，你必须以某种方式返回你的指针_551162 . 你无法向它发送一个指向堆栈上的 stringItem 的指针（即一个局部变量），就像你正在做的那样 .

    回复于

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