Read multiple .dat files in C++

Question

I used the code below to read one .dat file and find the execution time, it worked very well. I tried to build a loop to read multiple files as I have more than 20 files with different names (I need to keep their names), but it did not work. How can I develop this code to read all files located in a certain folder no matter how many they are? (based on following code)

#include <Windows.h>
#include <ctime>
#include <stdint.h>
#include <iostream>
using std::cout;
using std::endl;
#include <fstream>
using std::ifstream;

#include <cstring>

/* Returns the amount of milliseconds elapsed since the UNIX epoch. Works on both
 * windows and linux. */

uint64_t GetTimeMs64()
{


 FILETIME ft;
 LARGE_INTEGER li;

 /* Get the amount of 100 nano seconds intervals elapsed since January 1, 1601 (UTC) and copy it
  * to a LARGE_INTEGER structure. */
 GetSystemTimeAsFileTime(&ft);
 li.LowPart = ft.dwLowDateTime;
 li.HighPart = ft.dwHighDateTime;

 uint64_t ret;
 ret = li.QuadPart;
 ret -= 116444736000000000LL; /* Convert from file time to UNIX epoch time. */
 ret /= 10000; /* From 100 nano seconds (10^-7) to 1 millisecond (10^-3) intervals */

 return ret;

}




const int MAX_CHARS_PER_LINE = 512;
const int MAX_TOKENS_PER_LINE = 20;
const char* const DELIMITER = "|";

int main()
{
  // create a file-reading object
  ifstream fin;
  fin.open("promotion.txt"); // open a file
  if (!fin.good()) 
    return 1; // exit if file not found

  // read each line of the file
  while (!fin.eof())
  {
    // read an entire line into memory
    char buf[MAX_CHARS_PER_LINE];
    fin.getline(buf, MAX_CHARS_PER_LINE);

    // parse the line into blank-delimited tokens
    int n = 0; // a for-loop index

    // array to store memory addresses of the tokens in buf
    const char* token[MAX_TOKENS_PER_LINE] = {}; // initialize to 0

    // parse the line
    token[0] = strtok(buf, DELIMITER); // first token
    if (token[0]) // zero if line is blank
    {
      for (n = 1; n < MAX_TOKENS_PER_LINE; n++)
      {
    token[n] = strtok(0, DELIMITER); // subsequent tokens
        if (!token[n]) break; // no more tokens
  }
}

    // process (print) the tokens
    for (int i = 0; i < n; i++) // n = #of tokens
      cout << "Token[" << i << "] = " << token[i] << endl;
    cout << endl;
  }
  uint64_t z = GetTimeMs64();
  cout << z << endl;
  system("pause");
}

Answer 1

For listing files in a directory on Windows, refer to this link:

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365200(v=vs.85).aspx

Notes about your code:

1. don't use fin.eof() to test the end of input, see why: eof of istream in C++

2. to read multiple files, remember fin.clear() before fin.close if you use the same fin to read multiple files.

UPDATE:

The following code prints out the files name in a directory D:\\Test. If you need absolute path for every file or files in subfolders, change GetFiles to do that. This is pretty straightforward according to the link I provided. The code is test on VS2012 Win7 Pro.

#include <windows.h>
#include <Shlwapi.h>

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;

#pragma comment(lib, "Shlwapi.lib")

int GetFiles(const string &path, vector<string> &files, const string &wildcard = "\\*")
{
    wstring basepath(path.begin(), path.end());
    wstring wpath = basepath + wstring(wildcard.begin(), wildcard.end());

    WIN32_FIND_DATA ffd;
    HANDLE hFind = INVALID_HANDLE_VALUE;
    DWORD dwError = 0;

    hFind = FindFirstFile(wpath.c_str(), &ffd);

    if (INVALID_HANDLE_VALUE == hFind) {
        // display error messages
        return dwError;
    }

    TCHAR buf[MAX_PATH];
    do {
        if (ffd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) {
            // directory
        } else {
            PathCombine(buf, basepath.c_str(), ffd.cFileName);
            wstring tmp(buf);
            files.push_back(string(tmp.begin(), tmp.end()));
        }
    } while (FindNextFile(hFind, &ffd));

    dwError = GetLastError();
    if (ERROR_NO_MORE_FILES != dwError) {
        // some errors
    }
    FindClose(hFind);
    return dwError;
}

int main()
{
    string path("D:\\Documents\\Visual Studio 2012\\Projects\\SigSpatial2013");
    vector<string> files;
    GetFiles(path, files);
    string line;
    ifstream fin;
    for (int i = 0; i < files.size(); ++i) {
        cout << files[i] << endl;

        fin.open(files[i].c_str());
        if (!fin.is_open()) {
            // error occurs!!
            // break or exit according to your needs
        }

        while (getline(fin, line)) {
            // now process every line
        }

        fin.clear();
        fin.close();
    }
}

Answer 2

I think it's easier:

1- if you factor out the code that reads a file and process its content into its own function:
void process_file( char* filename );
2- add a new function to list a directory's content: char** list_dir( char* dir );
3- combine the 2 functions in your main()

this makes for cleaner and more testable code

Answer 3

I agree with the suggestions to encapsulate this. On Windows the code looks like this

HANDLE h;
WIN32_FIND_DATA find_data;
h = FindFirstFile( "*.dat", & find_data );
if( h == INVALID_HANDLE_VALUE ) {
    // Error
    return;
}
do {
    char * s = find_data.cFileName;
            // Your code here
} while( FindNextFile( h, & find_data ) );
FindClose( h );