Creating and Using a Temporary File

The following example copies one file to another. The second file is an uppercase version of the first file.

The application opens the ORIGINAL.TXT file by using CreateFile. The application then retrieves a temporary file name with the GetTempFileName function and uses CreateFile to create the temporary file. The application reads 4K blocks into a buffer, converts the buffer contents to uppercase, and writes the converted buffer to the temporary file. When all of ORIGINAL.TXT has been written to the temporary file, the application closes both files and renames the temporary file to ALLCAPS.TXT by using the MoveFile function.

HANDLE hFile; 
 
HANDLE hTempFile; 
 
DWORD  dwBytesRead, dwBytesWritten, dwPos; 
 
char szTempName[MAX_PATH]; 
 
char buffer[4096]; 
 
// Open the existing file. 
 
hFile = CreateFile("ORIGINAL.TXT",  // file name 
    GENERIC_READ,                   // open for reading 
    0,                              // do not share 
    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 
} 
 
// Create a temporary file. 
 
GetTempFileName("\\TEMP", // dir. for temp. files 
    "NEW",                // temp. file name prefix 
    0,                    // create unique name 
    szTempName);          // buffer for name 

hTempFile = CreateFile((LPTSTR) szTempName,  // file name 
    GENERIC_READ | GENERIC_WRITE, // open for read/write 
    0,                            // do not share 
    NULL,                         // no security 
    CREATE_ALWAYS,                // overwrite existing file
    FILE_ATTRIBUTE_NORMAL,        // normal file 
    NULL);                        // no attr. template 

if (hTempFile == INVALID_HANDLE_VALUE) 
{ 
    ErrorHandler("Could not create temporary file."); 
} 
 
// Read 4K blocks to the buffer. 
// Change all characters in the buffer to uppercase. 
// Write the buffer to the temporary file. 

 
do 
{
    if (ReadFile(hFile, buffer, 4096, 
        &dwBytesRead, NULL)) 
    { 
        CharUpperBuff(buffer, dwBytesRead); 
 
        WriteFile(hTempFile, buffer, dwBytesRead, 
            &dwBytesWritten, NULL); 
    } 
} while (dwBytesRead == 4096); 
 
// Close both files. 
 
CloseHandle(hFile); 
CloseHandle(hTempFile); 
 
// Move the temporary file to the new text file.
 
if (!MoveFile(szTempName, "ALLCAPS.TXT")) 
{ 
    ErrorHandler("Could not move temp. file."); 
}