除了一些用于AVR微控制器的简单嵌入式编码之外，我对C编程很陌生。
最近，我一直在尝试编写一个简单的环形缓冲区来接收串行数据，并找到了一些似乎在大多数情况下都能正常工作的示例代码。但是有一个指针传递给一个函数，用于从环形缓冲区返回值。不用说我努力理解指针。
我附加了在Pelles C中完成的所有代码，这似乎有效，但我不确定我是否正在处理来自*pc函数的int buf_get(char *pc)指针。我能够使用附加的代码编译没有错误或警告。
有人请告诉我为*pc设置变量的正确方法吗？
到目前为止，我正在使用char FromBuffer[1];，但我认为它充其量只是草率。
/****************************************************************************
* *
* File : main.c *
* *
* Purpose : Console mode (command line) program. *
* *
* History : Date Reason *
* 8/28/2014 Ring Buffer Example *
* *
***************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <conio.h> //needed for _getch(),_getche() and _putch()
#include <time.h> //used by the random number generator to start seed based on time
//============================= Constants ===================================
#define BUFSIZE 16
//============================= Functions ===================================
void DumpBuffer(void); //Used to display buffer for debugging
void buf_init(void); //Ring Buffer initialization
int buf_put(char c); //Ring Buffer add function
int buf_get(char *pc); //Ring Buffer get fucntion
//============================= Global Variables=============================
char buf[BUFSIZE]; //ring buffer
char *pIn, *pOut, *pEnd; //pointers for buffer fucntions
char full; //fucntion value for buffer functions and control within
char FromBuffer[1];
int BufferInputStatus; //0 = FULL, 1 = OK
int BufferOutputStatus; //0 = EMPTY, 1 = OK
long InputPointerBase; //input pointer base value used during display of ring buffer
long OutputPointerBase; //output pointer base value used during display of ring buffer
/****************************************************************************
* *
* Function: main *
* *
* Purpose : Main entry point. *
* *
* History : Date Reason *
* 8/28/2014 Ring Buffer Example *
* *
***************************************************************************/
/****************************************************************************
MAIN function that does:
1)
2)
****************************************************************************/
int main(int argc, char *argv[])
{
char CharIn;
int RandomChar = 97; //used by random character generator
//int num_between_x_and_y = (rand() % (X - Y)) + Y;
int LastRandomChar =0; //used to prevent two random char repeats in a row
//tell the user the program has started
printf("Start \n");
//seed the random number generator
srand(time(NULL));
//initialize the ring buffer
buf_init();
//find the base address of the pointers
InputPointerBase = (long)(pIn);
OutputPointerBase = (long)(pOut);
printf("Base Address Input Pointer %x\n",(int)(InputPointerBase));
printf("Base Address Output Pointer %x\n",(int)(OutputPointerBase));
//Main loop that allows filling the buffer and removing from buffer
//User used "i" or "o" to add or remove to ring buffer
//User exits with "Q"
while ((CharIn = _getch()) != 'Q') // "_getch()" does not wait for CR to return key and has no cho
{
//add something to the input buffer
if (CharIn == 'i')
{
RandomChar = (rand() % (122 - 97)) + 97; //get a ramdom character
//Only add to ring buffer is not a ramdom repeat
if (RandomChar != LastRandomChar)
{
printf ("Adding to buffer ==> %c\n", RandomChar);
LastRandomChar = RandomChar;
BufferInputStatus = buf_put((char)(RandomChar)); //add character to ring buffer
}
}//end of IF "input"
//remove something from input buffer
if (CharIn == 'o')
{
BufferOutputStatus = buf_get(FromBuffer);
}
//Show what is in the buffer along with the input and output pointers
DumpBuffer();
//Diaply what came out of the buffer
printf("This was the output : %c\n",FromBuffer[0]);
//printf("Input Pointing to %x\n",(int)(pIn));
if (BufferInputStatus == 1) printf("Buffer Input Status is OK\n");
else printf("Buffer Input Status is FULL\n");
if (BufferOutputStatus == 1) printf("Buffer Output Status is OK\n");
else printf("Buffer Output Status is EMPTY\n");
}//end of "While !='Q' "
printf("Exit \n");
return 0;
}
void DumpBuffer(void)
{
char BufferLocation = 0;
char InputPointerValue = 0;
char OutputPointerValue = 0;
//Display the buffer pointers and buffer content
for (BufferLocation = 0; BufferLocation < BUFSIZE; BufferLocation++)
{
//Show the location of the input pointer
InputPointerValue = (char)(pIn - InputPointerBase);
if (BufferLocation == InputPointerValue) printf("%-3s",">>>");
else printf("%-3s","");
//Show the buffer location
printf(":%-3d:",BufferLocation);
//Display what is in the buffer at that location
printf(":%-3c:",buf[BufferLocation]);
//Show the location of the output pointer
OutputPointerValue = (char)(pOut - OutputPointerBase);
if (BufferLocation == OutputPointerValue) printf("%-3s",">>>");
else printf("%-3s","");
//end the displayed line with a CR-LF
printf("\n");
}//End of FOR-LOOP for printing buffers
}//end of "DumpBuffer"
/****************************************************************************
* Raw example code from: *
* Example code from: *
* http://stackoverflow.com/questions/827691/how-do-you-implement-a-circular-buffer-in-c
* *
* No changes were made!!!! *
* *
****************************************************************************/
// init
void buf_init(void)
{
pIn = pOut = buf; // init to any slot in buffer
pEnd = &buf[BUFSIZE]; // past last valid slot in buffer
full = 0; // buffer is empty
}
// add char 'c' to buffer
int buf_put(char c)
{
if (pIn == pOut && full)
return 0; // buffer overrun
*pIn++ = c; // insert c into buffer
if (pIn >= pEnd) // end of circular buffer?
pIn = buf; // wrap around
if (pIn == pOut) // did we run into the output ptr?
full = 1; // can't add any more data into buffer
return 1; // all OK
}
// get a char from circular buffer
int buf_get(char *pc)
{
if (pIn == pOut && !full)
return 0; // buffer empty FAIL
*pc = *pOut++; // pick up next char to be returned
if (pOut >= pEnd) // end of circular buffer?
pOut = buf; // wrap around
full = 0; // there is at least 1 slot
return 1; // *pc has the data to be returned
}
答案 0 :(得分：2)
你问：
有人请告诉我为* pc设置变量的正确方法吗？
查看您的代码以及您如何使用FromBuffer，我会说：
FromBuffer。在main中，声明一个变量
char fromBufferChar;
将您使用FromBuffer的两个地方的fromBufferChar替换为 BufferOutputStatus = buf_get(FromBuffer);
。
更改
BufferOutputStatus = buf_get(&fromBufferChar);
到
printf("This was the output : %c\n",FromBuffer[0]);
更改
printf("This was the output : %c\n",fromBufferChar);
到
{{1}} 答案 1 :(得分：1)
首先我们尝试一些简单的事情，使用指针为变量赋值：
char c;
char *p;
p = &c;
*p = 'x';
然后我们做同样的事情，但将指针传递给执行动作的函数：
void foo(char *a)
{
*a = 'z';
}
...
char c;
char *p;
p = &c;
foo(p);
我们也可以取消不必要的指针变量：
char c;
foo(&c);
现在使用数组元素：
char m[5];
char *p;
p = &m[0];
*p = 'j';
数组变量的值是第一个元素的地址，因此我们可以这样做：
char m[5];
char *p;
p = m;
*p = 'j';
因此我们可以这样使用这个功能：
char m[5];
char *p;
p = m;
foo(p);
或者这样：
char m[5];
foo(m);
这能说清楚吗？