如何找到分段错误的来源？ （CS50：recover.c）

Question

我正在尝试在CS中创建一个用于从.raw文件中恢复JPG的程序（一次读取512个字节并查看它是否以JPG内容开头），但它会保留分段错误。我该如何判断问题的根源是什么？多谢你们！ （这是我的代码供参考）

      /**
 * recover.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Recovers JPEGs from a forensic image.
 */

 //0xff 0xd8 0xff 0xe0
 //0xff 0xd8 0xff 0xe1

#define BLOCK 512
#define START1END 0xe0
#define START2END 0xe1

#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>
#include <stdint.h>

//making variables
int found = 0; 
char* title;
FILE* img;
int ifopen = 1;

int main(int argc, char* argv[])
{
    //opening file
    FILE* inptr = fopen("card.raw", "r");
    //checking if file opening failed
    if (inptr == NULL)
    {
        return 2;
    }
    //sets the begins or jpgs
    uint8_t checkjpg1[4] = {0xff, 0xd8, 0xff, 0xe0};
    uint8_t checkjpg2[4] = {0xff, 0xd8, 0xff, 0xe1};

    //making buffer
    unsigned char buffer[512];

    //going through the file
    while(fread(&buffer,sizeof(char),BLOCK,inptr) == BLOCK)
    {
         //checking if begin == the possible begin of jpg    
         if ((buffer[0] == checkjpg1[0] && buffer[1] == checkjpg1[1] && buffer[2] == checkjpg1[2]) && 
         (buffer[3] == checkjpg1[3] || buffer[3] == checkjpg2[3]))
         {
            //if a jpg is not open
            if (ifopen == 1)
            {
                //make one
                found+=1;
                sprintf(title,"00%d",found);
                img = fopen(title,"a");
            }
            else//else
            {
                //end the one and open new one
                fclose(img);
                sprintf(title,"00%d",found);
                img = fopen(title,"a");
            }
         }
         else if(img != NULL)
         {
             fwrite(buffer,sizeof(char),BLOCK,img);
         }
    }

    fclose(inptr);
    free(buffer);
}

（抱歉长长的溢出线！）

Answer 1

在这一行（和其他人）中

sprintf(title,"00%d",found);

没有分配给title的内存，它被声明为

char *title;

但就是这样。

char title[BLOCK];

会更好。顺便提一下，在声明BLOCK应该

时，您不能使用buffer

unsigned char buffer[BLOCK];

另外，你需要另一个

found+=1;

在img代码块中打开else之前

。