c - 在 linux 中实现 rm 命令的 C 代码中的段错误

Question

这里有一段代码可以正常编译，但在运行时出现段错误。谁能告诉我如何解决这个问题。该代码在 C 中实现了 rm 系统调用。

#include<sys/stat.h>
#include<unistd.h>
#include<dirent.h>
#include<error.h>
#include <stdio.h>
#include <string.h>


int rmq(char*pth)
{
  char path[1000]; //hold the file name to be removed
  strcpy(path,pth);
  char *b; // stores the complete path of the file to be removed
  struct dirent *d;
  DIR *dir;

  char cwd[256]; //holds current working directory
  getcwd(cwd, sizeof(cwd));  
  dir = opendir(cwd);
  char path1[1000]; //for recursively moving through dir and subdir
  strcpy(path1,cwd);

  char newp[1000];
  struct stat buf;

  while((d = readdir(dir))) //if there are directories to be read 
  {  
     if(!strcmp(d->d_name,".") || !strcmp(d->d_name,"..")) // skip "." and ".."
     continue;

     //appends directory read to cwd

     strcpy(newp,path1); 
     strcat(newp,"/");
     strcat(newp,d->d_name); 
     //printf("%s>>",d->d_name);

     if(stat(newp,&buf)==-1) // puts file info in buf
        perror("stat");
     if(S_ISDIR(buf.st_mode))// if directory, then add a "/" to current path
     { 
     //if a directory then call function again(recursion)
        strcat(path1,"/");
        strcat(path1,d->d_name);
        rmq(path1);
     }
     else{ 
        //if directory current read is the one to be removed
        if((strcmp(path, d->d_name)) == 0){
        // append it with cwd & put it in b
        b = malloc(25 + strlen(d->d_name) + 1);
        sprintf(b, "%s/%s", "/home/urwa/Documents/OPS", d->d_name);
        remove(b); // remove that file
        free(b);
        }
     } 
 }
 return 0;
}


int main(){
   char cwd[256];
   getcwd(cwd, sizeof(cwd));

   char *argv[2];
   argv[1] = "dumbledore.txt";
   rmq(argv[1]); // file to be removed is passed as parameter
   return 0;
} 

我尝试了 malloc 但它没有解决问题

Answer 1

您绝对应该使用 -Wall -Wextra 标志编译您的代码，以便更好地受益于编译器帮助。在这里，使用您的代码您会收到以下警告:

test.c: In function ‘rmq’:
test.c:9:4: warning: implicit declaration of function ‘strcpy’ [-Wimplicit-function-declaration]
test.c:9:4: warning: incompatible implicit declaration of built-in function ‘strcpy’ [enabled by default]
test.c:25:3: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
test.c:26:3: warning: implicit declaration of function ‘strcmp’ [-Wimplicit-function-declaration]
test.c:30:5: warning: implicit declaration of function ‘strcat’ [-Wimplicit-function-declaration]
test.c:30:5: warning: incompatible implicit declaration of built-in function ‘strcat’ [enabled by default]
test.c:34:5: warning: implicit declaration of function ‘perror’ [-Wimplicit-function-declaration]
test.c:43:5: warning: implicit declaration of function ‘sprintf’ [-Wimplicit-function-declaration]
test.c:43:5: warning: incompatible implicit declaration of built-in function ‘sprintf’ [enabled by default]
test.c:43:5: warning: passing argument 1 of ‘sprintf’ makes pointer from integer without a cast [enabled by default]
test.c:43:5: note: expected ‘char *’ but argument is of type ‘char’
test.c:44:5: warning: implicit declaration of function ‘remove’ [-Wimplicit-function-declaration]
test.c: In function ‘main’:
test.c:58:2: warning: control reaches end of non-void function [-Wreturn-type]
test.c: In function ‘rmq’:
test.c:43:12: warning: ‘b’ may be used uninitialized in this function [-Wuninitialized]

因此，解决所有问题的最佳方法是执行以下操作:

• 首先，缺少的包括:

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

• 在 while 测试中的赋值周围添加额外的括号(编译器需要它来确保您知道自己在做什么):

  while((d = readdir(dir))){
  

• 您需要将 char b; 转换为 char *b; 并分配/取消分配必要的内存来存储字符串:

  if((strcmp(path, d->d_name)) == 0){
    b = malloc(25 + strlen(d->d_name) + 1);
    sprintf(b, "%s/%s", "/home/urwa/Documents/OPS", d->d_name);
    remove(b);
    free(b);
  }
  

• 然后，您需要在main 函数中添加return 0 以匹配您定义的签名。

完成所有这些后，仍然存在一个错误，因为您错过了一些案例。尝试使用 gdb 和/或 valgrind 修复它(考虑在编译时设置 -g 选项)。