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C语言中带队列的分段错误

segmentation-fault queue c

Trevor · 技术社区 · 16 年前

在将结构添加到队列中后,以下代码出现分段错误。

#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++;
}

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

5 回复 | 直到 16 年前

paxdiablo 16 年前

我认为你的问题在于:

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

你在缩放 next_index 但这是由第二个语句自动完成的- *(queue + (next_index)) 相当于 queue[next_index]

换句话说, 下一个索引 应为中的值 0 到 MAX_QUEUE-1 ,因此请尝试更改第一条语句以删除乘法 sizeof(struct myInfo) :

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++;
}

记住,你最终会溢出来的 queue_size 在你的无限循环中。你大概会检查以确保 队列大小

JSBÕ±Õ¸Õ£Õ¹ 16 年前

你在繁殖 next_index sizeof(struct myInfo) ,这是不必要的。添加到指针类型时,将根据指向的对象的大小自动计算偏移量。更改第一行 push() 应足够:

int next_index = (queue_size + queue_head) % MAX_QUEUE;

Thomas 16 年前

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++;
}

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);
        }
}

tomlogic 16 年前

*(queue + (next_index)) = info;

queue 是指向 struct myInfo . 你只需要在上面加1就可以得到下一个地址——你把它当作一个 char *

你可以这样做:

*(queue + queue_size++) = info;

smountcastle 16 年前

你可以请客队列作为一个数组,然后推送项目应该很简单:

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 */
   }
}