连续地址数据(数组或者malloc的内存)作为函数参数

在编程时，一簇连续的内存单元，比如数组或者malloc的内存块,如下的数组a 或者指针p.

int a[4];

int *p = malloc(4 * sizeof(int));

我们要想修改上述连续的内存块，可以写一个函数(一维指针做参数传入起始地址即可）来搞定。

If you want to pass a single-dimension array as an argument in a function, you would have to declare a formal parameter in one of following three ways and all three declaration methods produce similar results because each tells the compiler that an integer pointer is going to be received. Similarly, you can pass multi-dimensional arrays as formal parameters.

Way-1

Formal parameters as a pointer −

void myFunction(int *param) {...
}

Way-2

Formal parameters as a sized array −

void myFunction(int param[10]) {...
}

Way-3

Formal parameters as an unsized array −

void myFunction(int param[]) {...
}

1. 一维指针做参数

#include <stdio.h>
#define ARRAY_SIZE(arr) (sizeof(arr)/sizeof(arr[0]))void arrayDouble(int *p, int size)
{for (int i=0; i<size; i++){*(p+i) = *(p+i) * 2;}
}void arrayDouble1(int p[], int size)
{for (int i=0; i<size; i++){p[i] = p[i] * 2;}
}void arrayDouble2(int p[4], int size)
{for (int i=0; i<size; i++){p[i] = p[i] * 2;}
}int main()
{int arr[] = {1, 2, 3, 4};for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}printf("\n");arrayDouble(arr, ARRAY_SIZE(arr));for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}  printf("\n");arrayDouble1(arr, ARRAY_SIZE(arr));for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}printf("\n");arrayDouble2(arr, ARRAY_SIZE(arr));for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}printf("\n");return 0;
}

上述code运行结果：

1 2 3 4
2 4 6 8
4 8 12 16
8 16 24 32

2. 两维指针做参数

用两维数组做参数也可以一簇连续的内存单元的值，只是没有必要，大材小用，炫技而已，或者对指针操作含糊不清。

#include <stdio.h>
#define ARRAY_SIZE(arr) (sizeof(arr)/sizeof(arr[0]))void arrayDouble(int **pp, int size)
{int *p = *pp;for (int i=0; i<size; i++){*(p+i) = *(p+i) * 2;}
}/* arrayDouble1 is the same as arrayDouble,just without temp variable */
void arrayDouble1(int **pp, int size)
{for (int i=0; i<size; i++){*(*pp+i) = *(*pp+i) * 2;}
}int main()
{int arr[] = {1, 2, 3, 4};int *p = &arr[0];for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}printf("\n");arrayDouble(&p, ARRAY_SIZE(arr));for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);} printf("\n");arrayDouble1(&p, ARRAY_SIZE(arr));for (int i=0; i<ARRAY_SIZE(arr); i++){printf("%d ", arr[i]);}  printf("\n");return 0;
}

运行结果：

1 2 3 4
2 4 6 8
4 8 12 16