Creating and Opening Files - Win32 Programmer's Reference

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Creating and Opening Files

You can use the CreateFile function to create a new file or open an existing file. You must specify the filename, preferred access, share mode, creation instructions, and attributes.

In the following example, CreateFile opens an existing file for reading.

HANDLE hFile;

hFile = CreateFile("MYFILE.TXT", // open MYFILE.TXT

GENERIC_READ, // open for reading

FILE_SHARE_READ, // share for reading

NULL, // no security

OPEN_EXISTING, // existing file only

FILE_ATTRIBUTE_NORMAL, // normal file

NULL); // no attr. template

if (hFile == INVALID_HANDLE_VALUE) {

ErrorHandler("Could not open file."); /* process error */

}

In this example, CreateFile succeeds only if a file named MYFILE.TXT already exists in the current directory. An application should check the return value of CreateFile before attempting to use the handle to access the file. If an error occurs, the application should use the GetLastError function to get extended error information and respond accordingly.

A file must be closed before it can be deleted. The following lines close and delete the MYFILE.TXT file.

CloseHandle(hFile);

DeleteFile("MYFILE.TXT");

In the following example, CreateFile creates a new file and opens it for writing.

HANDLE hFile;

hFile = CreateFile("MYFILE.TXT", // create MYFILE.TXT

GENERIC_WRITE, // open for writing

0, // do not share

NULL, // no security

CREATE_ALWAYS, // overwrite existing

FILE_ATTRIBUTE_NORMAL | // normal file

FILE_FLAG_OVERLAPPED, // asynchronous I/O

NULL); // no attr. template

if (hFile == INVALID_HANDLE_VALUE) {

ErrorHandler("Could not open file."); // process error

}

In addition to the standard attributes (read only, hidden, system, and so on), you can also specify security attributes by including a pointer to a SECURITY_ATTRIBUTES structure as the fourth parameter. However, the underlying file system must support security for these attributes for them to have any effect. For more information about security, see Security.

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