传递一个动态数组中的功能用C [英] Passing a dynamic array in to functions in C

问题描述

我试图创建一个函数，它接受一个数组作为参数，增加值，它（增加它的大小，如果需要的话），并返回的项目数。
到目前为止，我有：

I'm trying to create a function which takes an array as an argument, adds values to it (increasing its size if necessary) and returns the count of items. So far I have:

int main(int argc, char** argv) {
    int mSize = 10;
    ent a[mSize];
    int n;
    n = addValues(a,mSize);

    for(i=0;i<n;i++) {
       //Print values from a
    }
}

int addValues(ent *a, int mSize) {
    int size = mSize;

    i = 0;

    while(....) { //Loop to add items to array
        if(i>=size-1) { 
            size = size*2;
            a = realloc(a, (size)*sizeof(ent));
        }
        //Add to array
        i++;
    }
    return i;
}

这工作，如果是MSIZE大到足以容纳阵列的所有潜在要素，但如果需要调整，我得到​​一个分段错误。

This works if mSize is large enough to hold all the potential elements of the array, but if it needs resizing, I get a Segmentation Fault.

我也尝试：

int main(int argc, char** argv) {
    ...
    ent *a;
    ...
}

int addValues(ent *a, int mSize) {
    ...
    a = calloc(1, sizeof(ent);
    //usual loop
    ...
}

要无果。

我想这是因为当我打电话的realloc的副本'一'在别处指出 - ？怎么可能修改该让'A'永远指向同一个位置

I assume this is because when I call realloc, the copy of 'a' is pointed elsewhere - how is it possible to modify this so that 'a' always points to the same location?

我要对这个正确？有没有更好的方式来处理在C动态结构？我应该实现一个链表来处理这些？

Am I going about this correctly? Are there better ways to deal with dynamic structures in C? Should I be implementing a linked list to deal with these?

推荐答案

这里的主要问题是，你正在尝试使用realloc的一个堆栈分配的数组。您有：

The main problem here is that you're trying to use realloc with a stack-allocated array. You have:

ent a[mSize];

这是在栈上自动分配。如果你想在这以后使用的realloc（），您将创建在使用堆的malloc（数组），就像这样：

That's automatic allocation on the stack. If you wanted to use realloc() on this later, you would create the array on the heap using malloc(), like this:

ent *a = (ent*)malloc(mSize * sizeof(ent));

这样的库的malloc（从而realloc的（）等）知道你的数组。从这个外观上来看，你可能会产生混淆 C99变长数组与真正的动态数组的，所以一定要试图解决这一问题前，理解上的差异在那里。

So that the malloc library (and thus realloc(), etc.) knows about your array. From the looks of this, you may be confusing C99 variable-length arrays with true dynamic arrays, so be sure you understand the difference there before trying to fix this.

真的，不过，如果你用C编写动态数组，你应该尝试使用OOP十岁上下的设计，封装有关阵列的信息，并从用户隐藏。你想了解你的阵列信息（例如指针和大小）整合到一个结构和操作（例如分配，添加元素，删除元素，释放等）到符合结构工作的特殊功能。所以，你可能有：

Really, though, if you are writing dynamic arrays in C, you should try to use OOP-ish design to encapsulate information about your arrays and hide it from the user. You want to consolidate information (e.g. pointer and size) about your array into a struct and operations (e.g. allocation, adding elements, removing elements, freeing, etc.) into special functions that work with your struct. So you might have:

typedef struct dynarray {
   elt *data;
   int size;
} dynarray;

和您可以定义某些功能dynarrays工作：

And you might define some functions to work with dynarrays:

// malloc a dynarray and its data and returns a pointer to the dynarray    
dynarray *dynarray_create();     

// add an element to dynarray and adjust its size if necessary
void dynarray_add_elt(dynarray *arr, elt value);

// return a particular element in the dynarray
elt dynarray_get_elt(dynarray *arr, int index);

// free the dynarray and its data.
void dynarray_free(dynarray *arr);

这样，用户不必记得到底如何分配的事物或什么大小的阵列当前。希望得到您开始。

This way the user doesn't have to remember exactly how to allocate things or what size the array is currently. Hope that gets you started.

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