Question

我没有收到以下字符串输出：

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);

Answer 1

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.
}

Answer 2

您在 malloc 调用中缺少终止空字符。

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

strlen 为您提供不包含终止空字符的大小。

此致

Answer 3

您将一个指向stringItem的指针传递给该函数，然后使用malloc的返回值覆盖该参数，然后将其丢弃，从而泄漏其内存。您有两种方法可以解决这个问题：

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);
}

或：

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malloc的指针。你不能像你一样向它发送一个指向堆栈stringItem的指针（即一个局部变量）。

Answer 4

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

，我应该会很好

无法正确访问Struct内容

4 个答案: