将值赋给while-loop内部的指针(使用< direct .h>)

Assignment of the values to the pointers inside while-loop (using <dirent.h>)

本文关键字：direct 使用 while-loop 内部 指针      更新时间：2023-10-16

假设我在文件夹c:/中有3个扩展名为".exe"的文件。我想创建3个char*类型的指针，每个指针都包含。exe文件的文件名。我们有3个指针，3个文件名。但真正让我困惑的是输出(见下文)。

我实现:

#include <dirent.h>
// some code here
DIR *dir;
struct dirent *ent;
char** FileName = new char* [3]; // Creating 3 pointers of type char*
count = 0; //counting the events when .exe file detected
dir = opendir("c:/");
while ((ent = readdir (dir)) != NULL) // read directory file by file until there is nothing
      {
            string matchName = string(ent->d_name);
            if (matchName.find(".exe") != std::string::npos) // Finding files with 
                                                             //.exe extension only
            {
               FileName[count] = ent->d_name;
               cout << "count = " << count << ": " << FileName[count] << endl;
               count++; // There are 3 .exe files in the folder, so the maximum
                        // of the count=3 (from FileName[0] to FileName[2])
            }
      }
closedir (dir);
// Here I'm just checking the output
cout << "count = 0: " << FileName[0] << endl;
cout << "count = 1: " << FileName[1] << endl;
cout << "count = 2: " << FileName[2] << endl;
我输出:

//from inside the while-loop:
count = 0: file0.exe
count = 1: file1.exe
count = 2: file2.exe
//from when I just check the output outside the loop        
count = 0:  // just empty for all 3 files
count = 1: 
count = 2:

为什么我期望赋值(至少，期望)当我在while-loop内，但当我检查循环外的指针的相同值-它只是空的?谢谢你！

这是一个问题:

FileName[count] = ent->d_name;

每次调用readdir都可能返回相同的ent，只是现在它指向的位置有不同的值。你应该把字符串复制出来，而不是指向这个临时存储区域。

最简单的方法是将FileName更改为:

std::string FileName[3];

虽然正确使用std::vector<std::string> FileName;不会花费更多的精力，但是您不需要限制3个文件。

也许你的数据被覆盖了?引用自readdir帮助:The data returned by readdir() may be overwritten by subsequent calls to readdir() for the same directory stream。所以，你应该复制char数组而不是赋值原始char指针

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