C中隊列出現分段錯誤

Question

將結構添加到我的隊列後，出現以下代碼的分段錯誤。

當MAX_QUEUE設置爲高電平時發生分段故障，但當設置爲低電平（100或200）時，不會發生錯誤。自從我上次用C語言編程以來，這已經有一段時間了，所以我希望有任何幫助。

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

#define MAX_QUEUE 1000 

struct myInfo { 
     char data[20]; 
}; 

struct myInfo* queue; 
void push(struct myInfo); 
int queue_head = 0; 
int queue_size = 0; 

int main(int argc, char *argv[]) 
{ 
     queue = (struct myInfo*) malloc(sizeof(struct myInfo) * MAX_QUEUE); 

     struct myInfo info; 
     char buf[10]; 
     strcpy(buf, "hello"); 

     while (1) 
     { 
       strcpy(info.data, buf); 
       push(info); 
     } 
} 

void push(struct myInfo info) { 
     int next_index = sizeof(struct myInfo) * ((queue_size + queue_head) % MAX_QUEUE); 
     printf("Pushing %s to %d\n", info.data, next_index); 
     *(queue + (next_index)) = info; 
     queue_size++; 
} 

輸出：

Pushing hello to 0 
Pushing hello to 20 
... 
Pushing hello to 7540 
Pushing hello to 7560 
Pushing hello to 7580 
Segmentation fault 

Answer 1

我覺得你的問題就在這裏：

int next_index = sizeof(struct myInfo) * ... 
*(queue + (next_index)) = info; 

你縮放next_index你的結構的大小，但是這是一件由第二自動完成聲明 - *(queue + (next_index))相當於queue[next_index]，後者對除我們之外的所有人都更易讀，因爲K & r爲首次發表:-)

換句話說，next_index值應當是一個從0到MAX_QUEUE-1，所以嘗試改變的第一個語句由sizeof(struct myInfo)刪除乘法：

void push(struct myInfo info) { 
    int next_index = (queue_size + queue_head) % MAX_QUEUE; 
    printf("Pushing %s to %d\n", info.data, next_index); 
    queue[next_index] = info; 
    queue_size++; 
} 

而且牢記你最終會在你的無限循環中溢出queue_size。您大概會檢查以確保queue_size在最終生產就緒代碼中的增量不會超過MAX_QUEUE，是的？

Answer 2

void push(struct myInfo info) { 
     int next_index = (queue_size + queue_head) % MAX_QUEUE; 
     printf("Pushing %s to %d\n", info.data, next_index); 
     queue[next_index] = info; 
     queue_size++; 
} 

而且，你並不需要該臨時buf：

int main(int argc, char *argv[]) 
{ 
     queue = (struct myInfo*) malloc(sizeof(struct myInfo) * MAX_QUEUE); 

     while (1) 
     { 
       struct myInfo info; /* Seems you're using C99 so we can declare here */ 
       strcpy(info.data, "hello"); 
       push(info); 
     } 
} 

Answer 3

你被sizeof(struct myInfo)乘以next_index，這是沒有必要的。添加到指針類型時，偏移量將根據指向對象的大小自動計算。改變push()第一行應足以：

int next_index = (queue_size + queue_head) % MAX_QUEUE; 

Answer 4

*(queue + (next_index)) = info; 

queue是指向一個struct myInfo。您只需要添加1即可獲取下一個地址 - 您將其視爲char *。

你可以這樣做：

*(queue + queue_size++) = info; 

Answer 5

你可以把隊列作爲一個數組，然後它應該是簡單的推項目：由於您使用的靜態大小

 
void push(struct myInfo info) { 
    if (queue_size < MAX_QUEUE) { 
    printf("Pushing %s to %d\n", info.data, queue_size); 
    queue[queue_size] = info; 
    queue_size++; 
    } else { 
    printf("ERROR: Queue is full.\n"); 
    /* alternatively you could have a queue_insertion_point 
     variable to keep track of where you are in the queue 
     and use that as your index into your array. You'd then 
     reset it to 0 (to wrap around) when it hit MAX_QUEUE. 
     You need to ensure you don't overwrite data currently 
     in the queue by comparing it against queue_head */ 
    } 
}