[英]discrepencies between gdb output and terminal output
我遇到了一個奇怪的問題。 我正在為基本上模仿生產者使用者問題的OS類制作一個共享內存fifo隊列。 在我的一個函數putBuffer()
,它向共享緩沖區插入了一個項目,在某個點之后,我沒有得到任何輸出,因此我通過gdb運行了它,它打印出我認為在初始終端運行以及退出gdb時會打印的內容它說程序正常退出,所以我不確定我的錯誤在哪里。 有沒有其他人經歷過這樣的事情?
因此,當我通過gdb運行它時,它會打印“經過初始檢查,而fifo->[12]
值只是在此處設置了硬編碼值以進行測試。但是在終端中,它僅打印“使其經過初始檢查”校驗。 我什至確定該錯誤不在printf()
什么想法嗎? 繼承人代碼
int putBuffer(FIFO_QUEUE *fifo, int element)
{
printf("made it past initial check\n");
fifo->queue[12] = 23;
//insert the element at the next available position IFF there is one
if(printf("made it to putBuffer and fifo->queue[12] = %d\n", fifo->queue[12]) < 0)
{
printf("error in putBuffer\n");
return -1;
}
//determine whether or not we need to "wrap" around to the beginning of the queue
if(fifo->putPos == fifo->size - 1)
fifo->putPos = 0; //wrap to the beginning
else
fifo->putPos++;
//increment the number of items in the queue
fifo->numItems++;
//if all went well return 0
return 0;
}
每個請求在這里是FIFO_QUEUE的定義,我在另一個函數中動態分配隊列結構,但是它存儲值並通過gdb打印
typedef struct fifoQueue{
int *queue;
int putPos; //next position to insert to
int rmPos; //next position to remove from
int numItems; //number of items currently in the queue
int size; //the max size of the queue
}FIFO_QUEUE;
這是我想出錯的地方,我需要在函數中動態分配fifo隊列,而我想做的是使用memcpy基本上創建一個fifo隊列,然后將其內容復制到共享內存中,但是似乎由於FIFO_QUEUE中的int *而導致斷開連接,我無法弄清楚。 我要去哪里了 我懷疑這與mkBuffer()函數中的動態分配有關,我的想法是memcpy只會復制其中的100字節,但是我可能會誤會
code for dynamic allocation
#include<sys/ipc.h>
#include<sys/shm.h>
#include<sys/types.h>
#include<stdlib.h>
#include<stdio.h>
#include <fcntl.h> /* For O_* constants */
#include <sys/stat.h>
#include<string.h>
#include "fifoQueue.h"
FIFO_QUEUE *makeBuffer(int size);
int main(int argc, char *argv[])
{
//our buffer
int i = 0;
int segment_id = 0;
FIFO_QUEUE *sharedBuff;
FIFO_QUEUE *fifo = NULL;
fifo = makeBuffer(25);
//-------retrieve COMMAND LINE arguments------//
if(argc != 2)
{
printf("getBuffer requires 2 command line args\n");
exit(-1);
}
//------SET UP SHARED MEMORY--------//
//get memory ID
segment_id = atoi(argv[1]);
printf("MAKE_BUFFER: Shared mem seg Id in get buffer = %d\n", segment_id);
//Attach
sharedBuff = (FIFO_QUEUE*)shmat(segment_id, NULL, SHM_RND);
//COPY contents of fifo into shared mem
memcpy((void*)sharedBuff, (void*)fifo, 120);
//--------CLEANUP--------//
//DETACH shared mem
shmdt(sharedBuff);
//deallocate memory
rmBuffer(fifo);
return 0;
}
/* makeBuffer()
Description:
- Creates a FIFO buffer of integers of size <size>
*/
FIFO_QUEUE *makeBuffer(int size)
{
//variables
int i = 0;
FIFO_QUEUE *fifo = NULL;
//allocate room for our struct
fifo = (FIFO_QUEUE*)malloc(sizeof(FIFO_QUEUE));
//allocate room for our queue
fifo->queue = (int*)malloc(sizeof(int) * size);
//set the initial position and number of items in the queue to 0
fifo->putPos = 0;
fifo->rmPos = 0;
fifo->numItems = 5;
fifo->size = size;
//return our pointer
return fifo;
}
這個:
memcpy((void*)sharedBuff, (void*)fifo, 120); /* Why 120 ? */
將從fifo
復制120個字節:不會復制動態分配的fifo.queue
數組。 由於queue
所需的元素數是硬編碼的, FIFO_QUEUE
將FIFO_QUEUE
的定義FIFO_QUEUE
為:
typedef struct fifoQueue{
int queue[25];
int putPos; //next position to insert to
int rmPos; //next position to remove from
int numItems; //number of items currently in the queue
int size; //the max size of the queue: always 25
}FIFO_QUEUE;
並將memcpy()
更改為:
memcpy(sharedBuff, fifo, sizeof(*fifo));
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