重新分配结构数组会出错 - 下一个大小无效

Question

I am writting a program that creates an array of structs (dynamically allocated). The code works until the array needs to be enlarged and even after checking everything I could think of and trying all sorts of tips from SO, it doesn't seem to work. None of this , that , those or these solved it.

Here is the problematic part of code:

    struct distance {
    ...;
}   *dist;


int     main        ( void )
{
    unsigned int len_max      = 128;
    unsigned int current_size = len_max * sizeof(distance);
    unsigned int distN        = 0;       //counter
    dist = (distance*) malloc(sizeof(distance*) * len_max);  
    for(unsigned int k = 0; k < i; k++)
    {
        for(unsigned int l = k+1; l < i; l++)
        {
            if(distN*sizeof(distance) >= current_size) // bug here?
            {
                current_size = 2*(distN) * sizeof(distance*);
                dist = (distance*)realloc(dist, current_size);
            } 
            //... do stuff
            distN++;
        }    
    }
    return 0;
}

Notes: 1) I know x = realloc (x, ...) is a BAD practise, but this will be running in a school testing environment with no error handling options, so there is no point in making a tmp_ptr. 2) I also know that casting a malloc and realloc is not the cleanest approach, but again, it is a rigid school testing environment for C course and it compiles with g++ . This way the compiler doesn't give me warnings.

EDIT: The code compiles, runs without issue when reallocation isn't needed. Once the input data exceeds memory allocated by malloc, this shows:

realloc(): invalid next size
Aborted (core dumped)

Answer 1

Your actual allocation is for array of pointers, not array of structs. If you want to make room for say n distance objects, you should call malloc( sizeof(distance) * n) while all I can see is malloc( sizeof(distance*) ...) . As your struct is probably greater in size than a pointer, there is not enough memory allocated.

Side note: realloc in double loop is bad idea. Try to do the math first, and use realloc only, if truly needed.