reading files in a directory C++ - c++

Question

I'm reading files in a directory and passing it to a function, I think I'm doing it in a wrong way, not able to figure out.
Here is my code first it reads files in a folder and send it to a function for further operations.
#include <dirent.h>
#include <stdio.h>
#include <vector>
#include <string>
#include <iostream>
using namespace std;
std::vector<std::string> fileName;
int main(void)
{
DIR *d;
struct dirent *dir;
vector<string> fileList;
int i=0;
d = opendir("files");
if (d)
{
while ((dir = readdir(d)) != NULL)
{
i++;
fileList.push_back(dir->d_name);
}
for(int i=0;i<fileList.size();i++) {
cout<<fileList[i]<<endl;
doSomething(fileList[i]);
}
closedir(d);
}
return(0);
}
int doSomething(fileName) {
//do something
}
Error
main.cpp: In function ‘int main()’:
main.cpp:29:28: error: ‘doSomething’ was not declared in this scope
doSomething(fileList[i]);
^
main.cpp: At global scope:
main.cpp:37:26: error: cannot convert ‘std::vector<std::basic_string<char> >’ to ‘int’ in initialization
int doSomething(fileName) {
^
main.cpp:37:28: error: expected ‘,’ or ‘;’ before ‘{’ token
int doSomething(fileName) {
^

Answer 1

Since your doSomething function is defined after main, it is not visible, that causes the first error. The correct way would be to at least declare the function first:
int doSomething(); //declaration
int main()
{
doSomething(); //now the function is declared
}
//definition
int doSomething()
{
}
Now, the second and third errors is emited because you didn't include the fileName parameter's type in your function definition. Based on your code, it should be a string:
int doSomething(string fileName)
{
}
I also noticed that, while this function returns int, you are not using it's returned value. Nevertheless, don't forget to return something from doSomething, otherwise it will cause undefined behavior.

Answer 2

Yes, Boost is great, but it's a bit bloaty. So, just for completenessapplied to reading images in a directory for OpenCV:
// you need these includes for the function
//#include <windows.h> // for windows systems
#include <dirent.h> // for linux systems
#include <sys/stat.h> // for linux systems
#include <algorithm> // std::sort
#include <opencv2/opencv.hpp>
#include <iostream> //cout
using namespace std;
/* Returns a list of files in a directory (except the ones that begin with a dot) */
int readFilenames(std::vector<string> &filenames, const string &directory)
{
#ifdef WINDOWS
HANDLE dir;
WIN32_FIND_DATA file_data;
if ((dir = FindFirstFile((directory + "/*").c_str(), &file_data)) == INVALID_HANDLE_VALUE)
return; /* No files found */
do {
const string file_name = file_data.cFileName;
const string full_file_name = directory + "/" + file_name;
const bool is_directory = (file_data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;
if (file_name[0] == '.')
continue;
if (is_directory)
continue;
filenames.push_back(full_file_name);
} while (FindNextFile(dir, &file_data));
FindClose(dir);
#else
DIR *dir;
class dirent *ent;
class stat st;
dir = opendir(directory.c_str());
while ((ent = readdir(dir)) != NULL) {
const string file_name = ent->d_name;
const string full_file_name = directory + "/" + file_name;
if (file_name[0] == '.')
continue;
if (stat(full_file_name.c_str(), &st) == -1)
continue;
const bool is_directory = (st.st_mode & S_IFDIR) != 0;
if (is_directory)
continue;
// filenames.push_back(full_file_name); // returns full path
filenames.push_back(file_name); // returns just filename
}
closedir(dir);
#endif
std::sort (filenames.begin(), filenames.end()); //optional, sort the filenames
return(filenames.size()); //Return how many we found
} // GetFilesInDirectory
void help(const char **argv) {
cout << "\n\n"
<< "Call:\n" << argv[0] << " <directory path>\n\n"
<< "Given a directory of images, create a vector of\n"
<< "their names, read and display them. Filter out\n"
<< "non-images\n"
<< endl;
}
int main( int argc, const char** argv )
{
if(argc != 2) {
cerr << "\nIncorrect number of parameters: " << argc << ", should be 2\n" << endl;
help(argv);
return -1;
}
string folder = argv[1];
cout << "Reading in directory " << folder << endl;
vector<string> filenames;
int num_files = readFilenames(filenames, folder);
cout << "Number of files = " << num_files << endl;
cv::namedWindow( "image", 1 );
for(size_t i = 0; i < filenames.size(); ++i)
{
cout << folder + filenames[i] << " #" << i << endl;
cv::Mat src = cv::imread(folder + filenames[i]);
if(!src.data) { //Protect against no file
cerr << folder + filenames[i] << ", file #" << i << ", is not an image" << endl;
continue;
}
cv::imshow("image", src);
cv::waitKey(250); //For fun, wait 250ms, or a quarter of a second, but you can put in "0" for no wait or -1 to wait for keypresses
/* do whatever you want with your images here */
}
}