Read multiple .dat files in C++ - 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:
don't use fin.eof() to test the end of input, see why: eof of istream in C++
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 );