Question

我一直在使用指针和malloc，我不知道如何正确使用free（）。我有一个程序，允许用户在选择特定选项时添加数据记录。我的程序只允许此功能发生一次，然后我得到一个段错误。我不认为我正在使用free（），并希望有人可以指出我的问题。我有全局变量：

int records = 5;
int access = 0;                  //initialize access counter to 0
int count = 0;

struct childrensBook *first;    //initialize first pointer
struct childrensBook *last;     //initialize last pointer
struct childrensBook *temp;     //initialize temp pointer

然后我开始使用主要功能，其中包含预定义记录：

int main(void)
{
    last = (struct childrensBook *) malloc(records * sizeof(struct childrensBook));     //allocate memory to "last" pointer
    first = last;       

    memcpy(last->title, "We're Going on a Bear Hunt", 27);                              //Beginning of all predefined Records
    memcpy(last->author, "Michael Rosen", 14);
    last->price = 7.99;
    last++;                                                                             //incrememnts pointer
    count = count + 1;                                                                  //begins counting of records

    memcpy(last->title, "Goodnight Moon", 15);
    memcpy(last->author, "Margaret Wise Brown", 20);
    last->price = 8.99;
    last++;                                                                             //incrememnts pointer
    count = count + 1;                                                                  //adds 1 to record count

    memcpy(last->title, "One Fish\n Two Fish\nRed Fish\n Blue Fish", 38);
    memcpy(last->author, "Dr. Seuss", 10);
    last->price = 8.99;
    last++;                                                                             //incrememnts pointer
    count = count + 1;                                                                  //adds 1 to record count

    memcpy(last->title, "Snowmen At Night", 17);
    memcpy(last->author, "Caralyn Buehner", 16);
    last->price = 16.99;
    last++;                                                                             //incrememnts pointer
    count = count + 1;                                                                  //adds 1 to record count

    memcpy(last->title, "Harold and the Purple Crayon", 29);
    memcpy(last->author, "Crockett Johnson", 17);
    last->price = 6.99

下面是我没有包含的菜单循环。我的问题在于我的添加功能，我在这里使用free（）：

   addRecord()                                                                          //Add Function
{                                                       
    last=first;                                                                         //get pointer in correct position
    memcpy(&temp, &last, records *sizeof(struct childrensBook));                        //use memcpy to copy info from last to temp

    fprintf(stderr, "\nYou have added the record:\n==========================\nBook: %s\nWritten by: %s\nPrice: $%.2f\n", temp->title, temp->author, 
        temp->price);

    temp++; 
    free(last);       //problem?? I have tried using free(first), free(last) and free(temp) and none work....
    count = count + 1;

}//end addRecord

我也是这样做的，它仍然不起作用：

            addRecord()                                                                                     //Add Function
    {                                                       
    last=first;                                                                         //get pointer in correct position
    temp = (struct childrensBook *) malloc(records * sizeof(struct childrensBook)); 
    memcpy(&temp, &last, records *sizeof(struct childrensBook));                        //use memcpy to copy info from last to temp

    fprintf(stderr, "\nYou have added the record:\n==========================\nBook: %s\nWritten by: %s\nPrice: $%.2f\n", temp->title, temp->author, 
        temp->price);

    temp++; 
    free(last);
    count = count + 1;

}//end addRecord

Answer 1

last指向first，在addRecord()的第一次通话结束时被释放。在第二次调用时，您将崩溃，因为last不再指向已分配的内存。但是，更有问题的是您没有为新记录分配任何新内存。请参阅realloc()。

使用malloc时如何正确使用free（）来释放内存？

1 个答案: