c - 如何使用指针在另一个函数中分配数组

Question

我是二年级计算机工程师，仍在学习 C 语言。我想了解如何使用函数而不是在 main 内部分配来动态分配数组。

这是当我在 main 中分配数组时有效的代码。

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <time.h>

#define ESC_KEY 27
#define NUM_1_KEY 49
#define NUM_2_KEY 50

void find_two_largest(int a[], int n, int *largest, int *second_largest);
void arrayInit(int *,int *, int, int);
void randGenArray(int [], int);
void inputArray(int[], int);
void result(int, int);
void loading(void);
int menu(void);

int main(void)
{
    system("color f5");
    int n,i,largest,largest_2, *a;

    arrayInit(a,&n, 2, 10);

    if(menu())
        randGenArray(a,n);
    else
        inputArray(a,n);

    find_two_largest(a,n,&largest,&largest_2);
    result(largest,largest_2);
    return 0;
}


void find_two_largest(int a[], int n, int *largest, int *second_largest)
{
    int i=0,j=0;
    system("cls");
    loading();
    *largest = 0;
    *second_largest = *largest;
    for (i=1;i<n;i++){
        if(*largest<a[i])
            *largest=a[i];
    }
    for(j=1;j<n;j++){
        if(*largest==a[j])
            continue;
        else{
            if(*second_largest<a[j])
                *second_largest=a[j];
        }
    }
    return;
}

void randGenArray(int a[], int n)
{
    srand(time(NULL));
    int i;
    for(i=0; i<n; i++){
        a[i]=rand()%100;
        Sleep(10);
        printf("\n>>  Integer %d: %d", i+1, a[i]);
    }
    printf("\n\n\nPress any key to continue...");
    getch();
    return;
}

void inputArray(int a[], int n)
{
    int i;
    for(i=0; i<n; i++){
        printf("\n  Please enter integer %d: ", i+1);
        scanf("%d",&a[i]);
    }
    return;
}

int menu(void)
{
    char _char;

    printf("\n  Please choose one of the following options:\n    1.Fill array manually\n    2.Fill array by random numbers\n\n  ");

    while(1)
    {
        _char = getch();
        switch(_char)
        {
            case ESC_KEY:
                printf("\n\n  Thank you for using our software!\n\n");
                exit(0);

            case NUM_1_KEY:
                system("cls");
                return 0;

            case NUM_2_KEY:
                system("cls");
                return 1;

            default:
                break;
        }
    }
}

void arrayInit(int *a,int *n, int min, int max)
{
    printf("\n  Please enter a length of the array: ");

    do{
    scanf("%d", n);
    if (*n<min||*n>max)
        printf("\nThe ranged is limited. Please enter the value between %d and %d.\n", min, max);
    } while(*n<min||*n>max);

    a = (int*)calloc(*n,sizeof(int));

    return;
}

void loading(void)
{
    printf("\n  Loading");
    printf(".");
    Sleep(300);
    printf(".");
    Sleep(300);
    printf(".");
    Sleep(300);
    system("cls");
    return;
}

void result(int l, int l2)
{
    system("cls");
    printf("\n  Largest = %d     Second Largest = %d",l,l2);
    Sleep(500);
    printf("\n\n\n  Thank you using our software! ;D\n\n");
    return;
}

但是如果您将此行从 arrayInit 剪切并粘贴到 main 并将 *n 更改为 n - 它会起作用!

a = (int*)calloc(*n,sizeof(int));

我很抱歉问了这么愚蠢和明显的事情，但我自己没有弄明白。感谢您的任何建议。

Answer 1

这是一个简单的程序，它将向您展示如何做到这一点 -

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

void create(int **p,int n);    // function taking arguments as int ** and n is number of elements

int main(void) {
   int *a;     
   int n=5,i;                       // declare and initialize n 
   create(&a,n);             // pass address of a to function
   for(i=0;i<n;i++){
        a[i]=i;                    // store value of i in a[i]
       printf("%d\n",i);          // print a[i]
    }
   free(a);                      // free the allocated memory
   return 0;
}

void create(int **p, int n){
      *p=calloc(n,sizeof(int));            // allocate memory to *p (type- is int *)
  }

Working Code