用C通用堆栈 [英] Generic Stacks in C

问题描述

我实现用C通用协议栈，我面临stackPop方法的问题。我的结构如下：

I am implementing generic stack in C and I am facing a problem in stackPop method. My struct is as follows:

Stack.h文件

        typedef struct{
            void *elems;
            int elemSize;
            int allocLength;
            int logLength;
            void (*freefnc)(void *);
        } Stack;

    void stackNew(Stack *s, int elemSize, void (*freefnc)(void *));
    void stackDispose(Stack *s);
    void stackPush(Stack *s, void *elemAddr);
    void stackPop(Stack *s, void *target);

Stack.c

    #inlcude<Stack.h>

    void stackNew(Stack *s, int elemSize, void (*freefnc)(void *)){
        s.allocLength = 4;
        s.logLength = 0;
        s.elemSize = elemSize;
        s.elems = malloc(4*elemSize);
        s.freefnc =  freefnc;
    }

    void stackDispose(Stack *s){
        if(s.freefnc!=NULL){
            for(int i=0; i<s.logLength; i++){
                freefnc((char *)s.elems+i*s->elemSize);
            }
        }
        free(s.elems);
    }

    void Stringfree(void *elem){
        free(*(char**)elem);
    }

    void stackPush(Stack *s, void *elemAddr){
        if(s.alloclength == s.logLength){
            stackGrow(s);
        }
        void *target = (char *)s.elems + s.logLength*s.elemSize;
        memcpy(target,elemAddr,s.elemSize);
        s.logLength++;
    }

    static void stackGrow(Stack *s){
        s.allocLength*=2;
        s.elems = realloc(s.elems, s.alloclength*s.elemSize);
        assert(s.elems!=NULL);
    }

    void stackPop(Stack *s, void *elemAddr){
        void *source = (char *)s.elems + (s.logLength-1)*s.elemSize;
        memcpy(elemAddr,source,s.elemSize);
        s.logLength--;
    }

我如何返回/获取价值正在 stackPop 功能弹出？我不想改变实现，但如果有这使相同的范围内实施尽可能，那么我会AP preciate一个好办法。其它方法也是可接受的。

How do I return/get the value being popped off in stackPop function? I do not want to change the implementation but if there is a good way which keeps the implementation same to the extent as much as possible, then I would appreciate that. Other approaches are also acceptable.

推荐答案

我认为你能做的最好的是返回一个指向弹出数据（以无效* 因为这是对你最好可以在C为通用的功能一样）：

I think the best you could do is to return a pointer to popped data (as a void* since that's about the best you can do in C for a 'generic' function):

void* stackPop(Stack *s, void *elemAddr){
        void *source = (char *)s.elems + (s.logLength-1)*s.elemSize;
        memcpy(elemAddr,source,s.elemSize);
        s.logLength--;
        return elemAddr;
}

请注意，调用者仍然需要提供存储器和数据弹出到的地址;如果你想编辑你可避免由具有功能的malloc（）内存

Note that the caller still needs to provide the memory and the address to pop the data into; if you want ed you could avoid that by having the function malloc() the memory:

void* stackPop(Stack *s){
        void *source = (char *)s.elems + (s.logLength-1)*s.elemSize;
        void *elemAddr = malloc(s.elemSize);
        // if (!elemAddr) handle_error();
        memcpy(elemAddr,source,s.elemSize);
        s.logLength--;
        return elemAddr;
}

当然，这需要调用者免费（）它时，它不再需要，并增加了需要处理的内存不足情况的轻微的并发症。

Of course that would require the caller to free() it when it is no longer needed, and adds the minor complication of needing to handle the out of memory situation.

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