c - ring/circular Buffer - 缓冲区实现并打印头部和尾部之间的值

Question

我是编程初学者，我在循环缓冲区的任务中有点陷入困境。我为我的环形缓冲区编写了函数push和pop，它应该如何工作，而且看起来它是有效的。但是当我使用pushBack通过每个元素实现dataBuffer并且在循环“for”中使用相同的方法时，我得到了不同的head值。在我的示例中可以看到(我只能在结构中使用 4 个值 + 添加第 5 个值来计算头和尾之间的元素数量):

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

    struct ringBuffer
    {
        int *bufferData;
        int head;
        int tail;
        int size;
        int num;
    };

    void bufferFree(struct ringBuffer *buffer)
    {
        free(buffer->bufferData);
    }

    void bufferInitialization(struct ringBuffer *buffer, int size)
    {
        buffer->size = size;
        buffer->head = 0;
        buffer->tail = 0;
        buffer->bufferData = (int*)malloc(sizeof(int) * size);
    }

    int pushBack(struct ringBuffer *buffer, int data)
    {
        buffer->bufferData[buffer->tail++] = data;
        if (buffer->tail == buffer->size)
        {
            buffer->tail = 0;
        }
        return 0;
    }

    int popFront(struct ringBuffer *buffer)
    {
        if (buffer->head != buffer->tail)
        {
            buffer->head++;
            if (buffer->head == buffer->size)
            {
                buffer->head = 0;
            }
        }
        return 0;
    }

    int bufferSize(struct ringBuffer *buffer)
    {
        //int numElements;
        //numElements = (buffer->size + buffer->head + buffer->tail) % buffer->size; // 8 + 0 + 6 % 8 = 6; 
        if (buffer->head >= buffer->tail)
        {
            return (buffer->head - buffer->tail);
        }
        else
        {
            return ((buffer->size - buffer->tail) + buffer->head);
        }

        /*if (buffer->head = !buffer->tail)
        {
        for (buffer->head = 0; buffer->head < buffer->tail; buffer->head++)
        {
        printf("head[%d] and tail[%d] --> bufferData = %d", buffer->head, buffer->tail, buffer->bufferData);
        }
        }*/
        return 0;
    }

    int printBuffer(struct ringBuffer *buffer)
    {
        int size = bufferSize((ringBuffer*)buffer->size);
        int i = buffer->head;
        while (buffer->size >= 0) 
        {
            if (!buffer->bufferData)
            {
                printf("Buffer is empty\n");
                return -1;
            }
            else if (i == buffer->size)
            {

        i = 0;
            }
            printf("    \n");
            buffer->size--;
        }
        /*printf("Values from HEAD to TAIL: ");
        if (buffer->head == buffer->tail)
        {
            printf("Head and tail are equals, not possible to show data\n");
        }
        else
        {
            printf("bufferData[%d] = %d\n", buffer->bufferData);
        }*/
    }

    int main(int argc, char* argv[])
    {
        struct ringBuffer buffer;
        int size = 8;
        int data[] = { 11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30 }; // 20 values
        int dataSize = sizeof(data) / sizeof(data[0]);
        bufferInitialization(&buffer, size);

        printf("1st implementation\n");
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        //printf("Current num elements = \n", bufferSize((ringBuffer*)buffer.num));

        printf("2nd implementation\n");
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        pushBack(&buffer, 10);  printf("head = %d, tail = %d\n", buffer.head, buffer.tail);
        bufferFree(&buffer);

        printf("\nInisialization\n");
        bufferInitialization(&buffer, size);
        printf("head = %d, tail = %d - then implementation\n", buffer.head, buffer.tail);
        for (int i = 0; i < dataSize; i++)
        {
            pushBack(&buffer, data[i]);
            printf("head = %d, tail = %d, dataBuffer = %d\n", buffer.head, buffer.tail, data[i]);
            popFront(&buffer);
        }
        printf("\nbufferData check:\n");
        for (int i = 0; i < size; i++)
        {
            printf("[%d] = %d  ", i, buffer.bufferData[i]);
        }
        printf("\nhead = %d, tail = %d\n", buffer.head, buffer.tail);

        bufferFree(&buffer);
        system("pause");
        return 0;
    }

我还必须编写一个函数来显示“head”和“tail”之间的元素数量。对于 for 循环，head 和 tail 之间始终有 1 个值，在第一个实现中 head 始终 = 0(并且当实现所有缓冲区时，head = tail)。这里的名称是bufferSize。我必须打印它。

如何解决这个 head 和 tail 问题以及如何编写正确的 printBuffer 函数？

谢谢

Answer 1

这显然是因为您的第一个和第二个实现不使用您在 for 循环中使用的 popFront(...) 函数而发生的。 popFront(...) 让您的头向前移动，很明显，如果您在同一个周期内推送和弹出数据，您的缓冲区中永远不会获得超过 1 条记录。