c - 函数指针作为 C 中结构的成员无效的初始值设定项

Question

这是我第一次在这里发帖，如果有什么不对的地方请指正。 好的，我得到了以下结构、函数和主函数:

typedef struct Integer50
{
// a dynamically allocated array to hold a 50
// digit integer, stored in reverse order
int *digits;
} Integer50;`

和

void big50Print(Integer50 *p)        //Unfortunately, I haven't made it to
{                                    //this part yet.  But once i get the
int i;                               //other function working, this should
if (p == NULL)                      //work fine, as it was given.
{
    printf("(null pointer)\n");
    return;
}
for (i = MAX50 - 1; i >= 0; i--)
    printf("%d", p->digits[i]);
printf("\n");
}

和

int main(void)
{
Integer50 *p;
big50Print(p = parseString("01234567890123456789012345678901234567890123456789"));
return 0;
}

我的目标是创建一个函数，将字符串向后解析为整数数组，并返回指向新分配的 Integer50 结构体的指针，如果内存分配失败或输入 str 为 NULL，则返回 NULL。到目前为止，我有这个:

Integer50 *parseString(char *str)   //This is the only one I can edit!
{
int len, i;
Integer50 *a[50]=malloc(sizeof(Integer50)); //this line is most likely wrong
                                            //And where the 'Invalid Initializer'
 len =strlen(str);                          //error is occuring

for (i=0; i<len; i++)            //This part works perfectly and
{                                //converts the string into integers
  a[i]= str[len-1-i]-'0';        //like it should.  The print statement here
 printf("a[%d]= %d, ", i, a[i]); //was just a test to make sure it worked.
}
 a->digits;               //also this line is probably wrong
    printf("\n");
 return a;
}

不幸的是，我还不太擅长使用指针，这被证明是相当困难的。如果有人能澄清我哪里出错了，我将不胜感激。谢谢!

Answer 1

这是您更正后的代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX50 50

typedef struct Integer50
{
// a dynamically allocated array to hold a 50
// digit integer, stored in reverse order
int *digits;
} Integer50;


void big50Print(Integer50 *p)        //Unfortunately, I haven't made it to
{                                    //this part yet.  But once i get the
int i;                               //other function working, this should
if (p == NULL)                      //work fine, as it was given.
{
    printf("(null pointer)\n");
    return;
}
for (i = MAX50 - 1; i >= 0; i--)
    printf("%d", p->digits[i]);
printf("\n");
}

Integer50 *parseString(char *str)   //This is the only one I can edit!
{
int len, i;
Integer50 *a =malloc(sizeof(Integer50)); //edited
a->digits = malloc(50 * sizeof(int));     //edited
 len =strlen(str);

for (i=0; i<len; i++)            //This part works perfectly and
{                                //converts the string into integers
  a->digits[i]= str[len-1-i]-'0';        //edited
 printf("a[%d]= %d, ", i, a->digits[i]); //edited
}
 a->digits;               //also this line is probably wrong
  printf("\n");
 return a;
}

int main(void)
{
Integer50 *p;
big50Print(p = parseString("01234567890123456789012345678901234567890123456789"));
return 0;
}

变化是

Integer50 *a[50]=malloc(sizeof(Integer50));

至

Integer50 *a =malloc(sizeof(Integer50));

因为您不需要一个 Integer50 数组，所以您需要一个 Integer50 内的整数数组。

所以我们在这行后面添加

a->digits = malloc(50 * sizeof(int));

同样

a->digits[i]= str[len-1-i]-'0';

另一个变化是在 printf 行中

printf("%d", p->digits[i]);

上一行将输出乱码。这将输出您存储在 int * 数字中的实际数据。 还要记住使用 free() 函数从堆中释放分配的内存。 希望有帮助!