[英]Create 2D array by passing pointer to function in c
So I read dozens of examples of passing an 2D array pointer to function to get/change values of that array in function. 所以我读了几十个将2D数组指针传递给函数的例子,以便在函数中获取/更改该数组的值。 But is it possible to create (allocate memory) inside the function.
但是可以在函数内创建(分配内存)。 Something like this:
像这样的东西:
#include <stdio.h>
void createArr(int** arrPtr, int x, int y);
int main() {
int x, y; //Dimension
int i, j; //Loop indexes
int** arr; //2D array pointer
arr = NULL;
x=3;
y=4;
createArr(arr, x, y);
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
printf("%d\n", arr[i][j]);
}
printf("\n");
}
_getch();
}
void createArr(int** arrPtr, int x, int y) {
int i, j; //Loop indexes
arrPtr = malloc(x*sizeof(int*));
for (i = 0; i < x; ++i)
arrPtr[i] = malloc(y*sizeof(int));
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
arrPtr[i][j] = i + j;
}
}
}
Forget about pointer-to-pointers. 忘记指针指针。 They have nothing to do with 2D arrays.
它们与2D阵列无关。
How to do it correctly: How do I correctly set up, access, and free a multidimensional array in C? 如何正确地做到这一点: 如何在C中正确设置,访问和释放多维数组? .
。
One of many reasons why it is wrong to use pointer-to-pointer: Why do I need to use type** to point to type*? 使用指针到指针是错误的众多原因之一: 为什么我需要使用类型**指向类型*? .
。
Example of how you could do it properly: 如何正确执行的示例:
#include <stdio.h>
#include <stdlib.h>
void* create_2D_array (size_t x, size_t y)
{
int (*array)[y] = malloc( sizeof(int[x][y]) );
for (size_t i = 0; i < x; ++i)
{
for (size_t j = 0; j < y; ++j)
{
array[i][j] = (int)(i + j);
}
}
return array;
}
void print_2D_array (size_t x, size_t y, int array[x][y])
{
for (size_t i = 0; i < x; ++i)
{
for (size_t j = 0; j < y; ++j)
{
printf("%d ", array[i][j]);
}
printf("\n");
}
}
int main (void)
{
size_t x = 5;
size_t y = 3;
int (*arr_2D)[y];
arr_2D = create_2D_array(x, y);
print_2D_array(x, y, arr_2D);
free(arr_2D);
return 0;
}
Yes, passing a pointer to int **
(but 3 stars is considered bad style), I suggest to return an allocated variable from your function: 是的,将指针传递给
int **
(但是3星被认为是坏的样式),我建议从函数返回一个已分配的变量:
int **createArr(int x, int y)
{
int **arrPtr;
int i, j; //Loop indexes
arrPtr = malloc(x*sizeof(int*));
if (arrPtr == NULL) { /* always check the return of malloc */
perror("malloc");
exit(EXIT_FAILURE);
}
for (i = 0; i < x; ++i) {
arrPtr[i] = malloc(y*sizeof(int));
if (arrPtr[i] == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < x; ++i) {
for (j = 0; j < y; ++j) {
arrPtr[i][j] = i + j;
}
}
return arrPtr;
}
Call it using: 用它来调用:
arr = createArr(x, y);
Yes, an array can be initialized this way. 是的,可以通过这种方式初始化数组。 As long as you pass a pointer, the memory address should remain the same.
只要传递指针,内存地址应保持不变。 So, if you assign anything to the pointer it will valid.
因此,如果您为指针指定任何内容,它将有效。
Think of an a[] as a* pointer to the first element 将a []视为指向第一个元素的*指针
a [][] will be a** pointer to a pointer of the first element or a pointer to the first array (first row of a table) a [] []将是指向第一个元素的指针的**指针或指向第一个数组的指针(表的第一行)
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