我正在完成一个循环缓冲区的工作，当它变满时需要加倍它。但是，我无法弄清楚如何将元素从旧缓冲区复制到新缓冲区中。我的代码如下：
#define startSize 10
#define fiveMin 300
cbuf* cbuf_init(){
cbuf *buffer = malloc(sizeof(cbuf) + 9 * sizeof(quote));
buffer->currSize = 0;
buffer->maxSize = startSize;
//buffer->startAt = 0;
buffer->start = 0;
buffer->end = 0;
buffer->freeSlots = startSize;
//buffer->currIndex = 0;
return buffer;
}
void cbuf_update(cbuf *cb_ptr, unsigned int time, double rate){
if(cb_ptr->freeSlots == 0){
printf("EXPANDING CIRCULAR BUFFER!\n");
cbuf *newBuffer = malloc(sizeof(cbuf) + 19 * sizeof(quote));
newBuffer->maxSize = cb_ptr->maxSize * 2;
newBuffer->start = cb_ptr->start;
newBuffer->end = cb_ptr->end;
newBuffer->freeSlots = newBuffer->maxSize - cb_ptr->maxSize;
int x;
for(x = 0; x < cb_ptr->maxSize; x ++){
printf("Copying from slot %d\n", x);
printf("Currently Copying time: %d\t Rate: %f\n", cb_ptr->quoteBuffer[x].time, cb_ptr->quoteBuffer[x].rate);
newBuffer->quoteBuffer[x].time = cb_ptr->quoteBuffer[x].time;
newBuffer->quoteBuffer[x].rate = cb_ptr->quoteBuffer[x].rate;
}
cb_ptr = newBuffer;
}
//If the start pointer has reached the end of the array and there are still free slots back at the beginning of the array, loop back.
if(cb_ptr->start == cb_ptr->maxSize && cb_ptr->freeSlots > 0){
cb_ptr->start = 0;
};
cb_ptr->quoteBuffer[cb_ptr->start].time = time;
cb_ptr->quoteBuffer[cb_ptr->start].rate = rate;
cb_ptr->start = cb_ptr->start +1;
cb_ptr->freeSlots = cb_ptr->freeSlots -1;
//If any quote in the array is older than 5 minutes when compared to the current quote, flag it as null and move the end pointer up one.
//Also, clear up a freeSlot.
int x;
for(x = cb_ptr->end; x < (cb_ptr->start); x ++){
if((time) - (cb_ptr->quoteBuffer[x].time) >= fiveMin){
cb_ptr->end = cb_ptr->end + 1;
cb_ptr->quoteBuffer[x].time = -1;
cb_ptr->quoteBuffer[x].rate = -1.00;
cb_ptr->freeSlots = cb_ptr->freeSlots +1;
}
}
}
void cbuf_dump(cbuf *cb_ptr){
printf("*****\t DUMPING \t*****\n");
if(cb_ptr->start > cb_ptr->end){
int x;
for(x = cb_ptr->end; x<(cb_ptr->start); x++){
printf("%d.) time = %d, \t rate = %f\n",x,(cb_ptr->quoteBuffer[x].time),(cb_ptr->quoteBuffer[x].rate));
}
}
/*
If the start pointer has been wrapped back around to the beginning of the circular buffer, then the end pointer must be at an index that is greater than the start index. For this, we need to print out the data ranging from the end pointer to the end of the array, and then the data from the start pointer to the end pointer provided the data isn't flagged as null (having -1 for both entries in the quote struct).
*/
if(cb_ptr->end > cb_ptr->start){
int x;
for(x=cb_ptr->end; x < cb_ptr->maxSize; x ++){
printf("%d.) time = %d, \t rate = %f\n",x,(cb_ptr->quoteBuffer[x].time),(cb_ptr->quoteBuffer[x].rate));
}
int y;
for(y = 0; y < cb_ptr->start; y ++){
if(cb_ptr->quoteBuffer[y].time != -1){
printf("%d.) time = %d, \t rate = %f\n",y,(cb_ptr->quoteBuffer[y].time),(cb_ptr->quoteBuffer[y].rate));
}
}
}
printf("freeslots = %d\n", cb_ptr->freeSlots);
}
int main(){
cbuf *cb1 ;
cb1 = cbuf_init() ;
cbuf_update(cb1, 60, 1.291) ;
cbuf_update(cb1, 63, 1.287) ;
cbuf_update(cb1, 63, 1.231) ;
cbuf_update(cb1, 69, 1.229) ;
cbuf_update(cb1, 72, 1.247) ;
//cbuf_dump(cb1);
cbuf_update(cb1,361,1.291);
//cbuf_dump(cb1);
cbuf_update(cb1, 411, 1.291) ;
//cbuf_dump(cb1);
cbuf_update(cb1, 412, 1.281) ;
cbuf_update(cb1, 413, 1.292) ;
cbuf_update(cb1, 414, 1.284) ;
//cbuf_dump(cb1);
cbuf_update(cb1, 414, 1.290) ;
//cbuf_dump(cb1);
//cbuf_update(cb1, 415, 1.290) ;
//cbuf_dump(cb1);
cbuf_update(cb1, 511, 1.241) ;
cbuf_update(cb1, 512, 1.251) ;
cbuf_update(cb1, 513, 1.232) ;
cbuf_update(cb1, 514, 1.202) ;
cbuf_update(cb1, 517, 1.119) ;
cbuf_dump(cb1);
return 0;
}
当它试图插入最后一个引号并且需要展开时，问题是主要的（最后一个引用是：
cbuf_update(cb1, 517, 1.119)
我的困惑是如何将newBuffer cbuf结构分配给cb_ptr缓冲区。它们都是指向cbuf的指针，但是如何将cb_ptr分配给newBuffer？
我的输出目前是：
EXPANDING CIRCULAR BUFFER!
Copying from slot 0
Currently Copying time: 414 Rate: 1.290000
Copying from slot 1
Currently Copying time: 511 Rate: 1.241000
Copying from slot 2
Currently Copying time: 512 Rate: 1.251000
Copying from slot 3
Currently Copying time: 513 Rate: 1.232000
Copying from slot 4
Currently Copying time: 514 Rate: 1.202000
Copying from slot 5
Currently Copying time: 361 Rate: 1.291000
Copying from slot 6
Currently Copying time: 411 Rate: 1.291000
Copying from slot 7
Currently Copying time: 412 Rate: 1.281000
Copying from slot 8
Currently Copying time: 413 Rate: 1.292000
Copying from slot 9
Currently Copying time: 414 Rate: 1.284000
***** DUMPING *****
freeslots = 0
答案 0 :(得分：2)
保存数组（衰减到指向其基数的指针），如果要修改它，包括指针，则必须通过地址传递 C中的所有。像其他任何东西一样，声明参数是一个指向你想要修改的类型的指针（在这种情况下，它将是指向指向cbuf的指针），然后传递调用者端指针的地址
我能为您的代码考虑的最小变化是：
void cbuf_update(cbuf **cb_pptr, unsigned int time, double rate)
{
// extract pointer value stored in in/out parameter
cbuf *cb_ptr = *cb_pptr;
if(cb_ptr->freeSlots == 0)
{
printf("EXPANDING CIRCULAR BUFFER!\n");
cbuf *newBuffer = malloc(sizeof(cbuf) + 19 * sizeof(quote));
newBuffer->maxSize = cb_ptr->maxSize * 2;
newBuffer->start = cb_ptr->start;
newBuffer->end = cb_ptr->end;
newBuffer->freeSlots = newBuffer->maxSize - cb_ptr->maxSize;
int x;
for(x = 0; x < cb_ptr->maxSize; x ++){
printf("Copying from slot %d\n", x);
printf("Currently Copying time: %d\t Rate: %f\n", cb_ptr->quoteBuffer[x].time, cb_ptr->quoteBuffer[x].rate);
newBuffer->quoteBuffer[x].time = cb_ptr->quoteBuffer[x].time;
newBuffer->quoteBuffer[x].rate = cb_ptr->quoteBuffer[x].rate;
}
free(cb_ptr);
*cb_pptr = cb_ptr = newBuffer;
}
//If the start pointer has reached the end of the array and there are still free slots back at the beginning of the array, loop back.
if(cb_ptr->start == cb_ptr->maxSize && cb_ptr->freeSlots > 0){
cb_ptr->start = 0;
};
cb_ptr->quoteBuffer[cb_ptr->start].time = time;
cb_ptr->quoteBuffer[cb_ptr->start].rate = rate;
cb_ptr->start = cb_ptr->start +1;
cb_ptr->freeSlots = cb_ptr->freeSlots -1;
//If any quote in the array is older than 5 minutes when compared to the current quote, flag it as null and move the end pointer up one.
//Also, clear up a freeSlot.
int x;
for(x = cb_ptr->end; x < (cb_ptr->start); x ++){
if((time) - (cb_ptr->quoteBuffer[x].time) >= fiveMin){
cb_ptr->end = cb_ptr->end + 1;
cb_ptr->quoteBuffer[x].time = -1;
cb_ptr->quoteBuffer[x].rate = -1.00;
cb_ptr->freeSlots = cb_ptr->freeSlots +1;
}
}
}
相信我，它不会得到更多的微小变化。不幸的是，您将不得不更改所有更新调用。没有绕过那个。他们将采取这种形式：
cbuf_update(&cb1, 60, 1.291);
如果你把这个东西放回呼叫者那边，正常免费：
free(cb1);
希望这是有道理的。绝对探索memcpy()的优点，用于实际的数据复制。它会使它变得更加混乱。