How to save ofn.lpstrFile to string properly? - c++

Question

Hi i am trying to make a GUI for image compare software. The idea is to choose a picture with OPENFILENAME, then get its address with ofn.lpstrFile then make a histogram for that image. So i use:
return(ofn.lpstrFile);
I can cout the address or write it to an .xml file and the address is correct, but when i am trying to do the histogram it gives me all zeros. Behaves like the address was invalid.
Any ideas ?
my code :
string path=browse(); //getting the string from ofn.lpstrFile
path.c_str();
replace(path.begin(), path.end(), '\\', '/'); //converting backslash to slash also may be the problem
HistCreation(path,root_dir);
and
void HistCreation(string path,string root_dir) {
Mat img;
img = imread(path); // here if i manually enter the address everything works fine, if I insert the path then loads empty image
.
.
.
I also tried
char * cstr = new char[path.length() + 1];
std::strcpy(cstr, path.c_str());
Did not work either

Answer 1

std::string returns the string and that's all you need. This is example to open a bitmap file.
(Edit)
#include <iostream>
#include <string>
#include <windows.h>
std::string browse(HWND hwnd)
{
std::string path(MAX_PATH, '\0');
OPENFILENAME ofn = { sizeof(OPENFILENAME) };
ofn.hwndOwner = hwnd;
ofn.lpstrFilter =
"Image files (*.jpg;*.png;*.bmp)\0*.jpg;*.png;*.bmp\0"
"All files\0*.*\0";
ofn.lpstrFile = &path[0];
ofn.nMaxFile = MAX_PATH;
ofn.Flags = OFN_FILEMUSTEXIST;
if (GetOpenFileName(&ofn))
{
//string::size() is still MAX_PATH
//strlen is the actual string size (not including the null-terminator)
//update size:
path.resize(strlen(path.c_str()));
}
return path;
}
int main()
{
std::string path = browse(0);
int len = strlen(path.c_str());
if (len)
std::cout << path.c_str() << "\n";
return 0;
}
Note, Windows uses NUL-terminated C-strings. It knows the length of the string by looking for the zero at the end.
std::string::size() is not always the same thing. We can call resize to make sure they are the same thing.
You shouldn't need to replace \\ with /. If your library complains about \\ then replace as follows:
Example:
...
#include <algorithm>
...
std::replace(path.begin(), path.end(), '\\', '/');
Use std::cout to examine the output instead of guessing if it worked or not. In Windows program you can use OutputDebugString or MessageBox to see what the string is.
HistCreation(path, root_dir);
I don't know what root_dir is supposed to be. If HistCreation fails or it has the wrong parameter then you have a different problem.