为什么readdir后stat不工作？ [英] Why is stat not working after readdir?

问题描述

我写了一个打印目录名或文件名的程序。这很容易，但我有麻烦。
无法区分目录和文件类型。我知道，我使用stat.st_mode完成它。但是有些错误：

当我使用gdb检查st_mode值时，我发现它是0 ， 除 。和..，所以这里是一个问题：为什么st_mode是0？

这是我的代码：

  #include< stdio.h> 
 #include< stdlib.h> 
 #include< dirent.h> 
 #include< sys / stat.h> 
 
 int main（void）
 {
 DIR * pDir = opendir（MyDirectory）; 
 struct dirent * pDirent; 
 struct stat vStat; 
 
 if（pDir == NULL）
 {
 printf（无法打开目录\MyDirectory\）; 
 exit（1）; 
 
 
 while（（pDirent = readdir（pDir））！= NULL）
 {
 stat（pDirent-> d_name，& vStat）; 
 if（S_ISDIR（vStat.st_mode））
 printf（Directory：％s\\\
，pDirent-> d_name）; 
 else 
 printf（File：％s\\\
，pDirent-> d_name）; 
} 
 
 closedir（pDir）; 
 return 0; 
} 
  

解决方案

经典 readdir 错误： pDirent-> d_name 是目录条目的名称，而不是文件的路径。它是1，4-5.c等等。所以你的 stat 呼叫正在当前目录中找到具有该名称​​的文件，而不是 MyDirectory 。

检查 stat 的返回值。你会看到它是 ENOENT - 除了。和 .. ，它也存在于当前目录中。当 stat 失败时，统计结构的内容未定义。

如果您在以外的目录中调用 opendir 。，然后做几乎任何有用的返回的名称，你需要建立一个完整的路径。将您传递给 opendir 的路径复制到具有足够空间的斜杠和文件名的缓冲区，并将每个文件名复制到该缓冲区。概念证明代码（错误检查等等）：

  char * directory =MyDirectory; 
 size_t directory_length = strlen（directory）; 
 char * path = malloc（directory_length + 1 + NAME_MAX）; 
 strcpy（path，directory）; 
 path [directory_length] ='/'; 
 while（（pDirent = readdir（pDir））！= NULL）{
 strcpy（path + directory_length + 1，pDirent-> d_name）; 
 if（stat（path，& vStat）== -1）{
 perror（path）; 
继续; 
} 
 ... 
} 
  

I wrote a program that print the directory name or file name. It's easy but I got something trouble. It couldn't distinguish directory and file type. I know and I used stat.st_mode to finish it. But something wrong:

when I use gdb to check the st_mode value, I found it was 0, except "." and "..", so here is the question: why st_mode is 0?

and that is my code:

#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/stat.h>

int main(void)
{
DIR *pDir = opendir("MyDirectory");
struct dirent *pDirent;
struct stat vStat;

if (pDir == NULL)
{
    printf("Can't open the directory \"MyDirectory\"");
    exit(1);
}

while ((pDirent = readdir(pDir)) != NULL)
{
    stat(pDirent->d_name, &vStat);
    if (S_ISDIR(vStat.st_mode))
        printf("Directory: %s\n", pDirent->d_name);
    else
        printf("File: %s\n", pDirent->d_name);
}

closedir(pDir);
return 0;
}

解决方案

Classic readdir mistake: pDirent->d_name is the name of the directory entry, not a path to the file. It's "1", "4-5.c", etc. So your stat calls are looking for a file with that name in the current directory, not under MyDirectory.

Check the return value of stat. You'll see that it's ENOENT — except for . and .., which exist in the current directory as well. When stat fails, the content of the stat structure is undefined.

If you're calling opendir in a directory other than ., then to do pretty much anything useful with the returned names, you need to build a full path. Copy the path you passed to opendir to a buffer with enough room for a slash and file name in addition, and copy each file name to that buffer. Proof-of-concept code (error checking omitted, etc.):

char *directory = "MyDirectory";
size_t directory_length = strlen(directory);
char *path = malloc(directory_length + 1 + NAME_MAX);
strcpy(path, directory);
path[directory_length] = '/';
while ((pDirent = readdir(pDir)) != NULL) {
    strcpy(path + directory_length + 1, pDirent->d_name);
    if (stat(path, &vStat) == -1) {
        perror(path);
        continue;
    }
    …
}

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