将指针传递给指针并重新分配空间

Question

我发布此示例代码以解释我的问题。我试图在函数间传递一个指向整数的指针。如果你编译&运行这个代码，你会看到奇怪的数字出现，我不明白为什么。我认为这是一个坏的使用realloc()。如果有人可以提供一个提示，或者可能会重定向我一些类似的问题，我会感激。我寻找这个问题，但我找不到任何类似的东西。

#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

您正在使用realloc不正确。重新分配的程度的大小必须

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; 
    //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
} 

程序输出是

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