CommDlg32: FileOpen Function

The CommDlg32.dll library provides a set of common dialog box functions that allow applications to interact with the user for tasks such as opening files, saving files, and choosing colors. The FileOpen function (often accessed via GetOpenFileName or GetSaveFileName) is a cornerstone for file selection.

Function Signature

This function displays the File Open common dialog box. This dialog box allows the user to select files and paths. The function returns TRUE if the user selects a file and the function successfully closes the dialog box, or FALSE if the user cancels the dialog box or an error occurs.

Parameters

OPENFILENAME Structure

The OPENFILENAME structure is crucial for configuring and receiving information from the File Open dialog. Key members include:

• lStructSize: The size of the structure in bytes.
• hwndOwner: A handle to the owner window of the dialog box.
• hInstance: Handle to the instance of the application that owns the dialog box.
• lpstrFilter: A pointer to a string that specifies the file types that can be selected. The string consists of pairs of null-terminated strings. The last pair must be terminated by two null characters (\0\0).
• lpstrFile: A pointer to a buffer that contains the name of the file selected by the user. This buffer must be large enough to hold the null-terminated file name.
• nMaxFile: The size, in characters, of the buffer pointed to by lpstrFile.
• lpstrTitle: A pointer to a null-terminated string that is placed in the title bar of the dialog box. If this member is NULL, the title bar contains the default title.
• Flags: A set of bit flags that specify various options for the dialog box.

Common Flags:

• OFN_EXPLORER: Use the new Explorer-style dialog box.
• OFN_FILEMUSTEXIST: The user must type a file name that exists.
• OFN_PATHMUSTEXIST: The user must type a path that exists.
• OFN_HIDEREADONLY: Hide the read-only check box.
• OFN_ALLOWMULTISELECT: Allows the user to select multiple files.

Return Value

Example Usage

#include <windows.h>
#include <commdlg.h>
#include <stdio.h>

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    OPENFILENAME ofn;
    char szFileName[MAX_PATH] = "";

    // Initialize OPENFILENAME structure
    ZeroMemory(&ofn, sizeof(ofn));
    ofn.lStructSize = sizeof(ofn);
    ofn.hwndOwner = NULL; // Or get the handle of your main window
    ofn.lpstrFilter = "Text Files (*.txt)\0*.txt\0All Files (*.*)\0*.*\0";
    ofn.lpstrFile = szFileName;
    ofn.nMaxFile = sizeof(szFileName);
    ofn.lpstrTitle = "Select a File";
    ofn.Flags = OFN_EXPLORER | OFN_FILEMUSTEXIST | OFN_PATHMUSTEXIST;

    // Display the File Open dialog box
    if (GetOpenFileName(&ofn)) {
        // User selected a file
        MessageBox(NULL, szFileName, "Selected File", MB_OK);
    } else {
        // User cancelled or an error occurred
        DWORD dwError = CommDlgExtendedError();
        if (dwError) {
            char errorMsg[100];
            sprintf(errorMsg, "Dialog Error: %lu", dwError);
            MessageBox(NULL, errorMsg, "Error", MB_ICONERROR);
        } else {
            MessageBox(NULL, "File selection cancelled.", "Cancelled", MB_OK);
        }
    }

    return 0;
}
            

Remarks

See Also