将指针传递给指针并重新分配 space

Question

我post这个示例代码是为了说明我的问题。我试图在函数之间传递一个指向整数的指针。如果你编译 & 运行这段代码，你会看到奇怪的数字出现，我不明白为什么。我认为 realloc() 的使用不当。如果有人可以提供提示或将我重定向到与此类似的一些问题，我将不胜感激。我搜索了这个问题，但找不到任何类似的问题。

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


void myFunction(int **output);


int main(){

    int *indices;
    myFunction(&indices);

    printf("{");
    for(int i=0;i<10;i++){//suppose also for some mysterious reasons that I know min_size in the main
        printf("%i,", indices[i]);
    }
    printf("}\n");

    return 0;
}


void myFunction(int **output){

    int size = 130;//allocating big amount of space
    int* indices = malloc(sizeof(int)*size);

    //...start doing mysterious stuffs....
    int min_size = 10; 
    for(int i=0;i<min_size;i++){
        indices[i] = i;//just for saving something
    }
    //...end doing mysterious stuffs...

    //now for some reasons I know I need only min_size elements and all other are wasting space so I reallocate
    indices = realloc(indices,min_size);//resizing in order to save space

    *output = indices;
}

Answer 1

您没有正确使用 realloc。重新分配范围的大小必须是

min_size * sizeof( int )

给你

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

void myFunction(int **output);


int main( void )
{

    int *indices;
    myFunction(&indices);

    printf("{");
    for(int i=0;i<10;i++){//suppose also for some mysterious reasons that I know min_size in the main
        printf("%i,", indices[i]);
    }
    printf("}\n");

    return 0;
}


void myFunction(int **output){

    int size = 130;//allocating big amount of space
    int* indices = malloc(sizeof(int)*size);

    *output = indices;
    // ^^^^^^^^^^^^^^^

    //...start doing mysterious stuffs....
    int min_size = 10; 
    for(int i=0;i<min_size;i++){
        indices[i] = i;//just for saving something
    }
    //...end doing mysterious stuffs...

    //now for some reasons I know I need only min_size elements and all other are wasting space so I reallocate

    indices = realloc(indices, min_size * sizeof( int ) );//resizing in order to save space
    //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    if ( indices ) *output = indices;
    //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
}

程序输出为

{0,1,2,3,4,5,6,7,8,9,}

将指针传递给指针并重新分配 space

Passing pointer to pointer and reallocate space

c

memory

pointers

realloc