WritePrivateProfileStringA function (winbase.h)

Copies a string into the specified section of an initialization file.

BOOL WritePrivateProfileStringA(
  [in] LPCSTR lpAppName,
  [in] LPCSTR lpKeyName,
  [in] LPCSTR lpString,
  [in] LPCSTR lpFileName
);

[in] lpAppName

The name of the section to which the string will be copied. If the section does not exist, it is created. The name of the section is case-independent; the string can be any combination of uppercase and lowercase letters.

[in] lpKeyName

The name of the key to be associated with a string. If the key does not exist in the specified section, it is created. If this parameter is NULL, the entire section, including all entries within the section, is deleted.

[in] lpString

A null-terminated string to be written to the file. If this parameter is NULL, the key pointed to by the lpKeyName parameter is deleted.

[in] lpFileName

The name of the initialization file.

If the file was created using Unicode characters, the function writes Unicode characters to the file. Otherwise, the function writes ANSI characters.

If the function successfully copies the string to the initialization file, the return value is nonzero.

If the function fails, or if it flushes the cached version of the most recently accessed initialization file, the return value is zero. To get extended error information, call GetLastError.

A section in the initialization file must have the following form:

[section]
key=string
      .
      .
      .

If the lpFileName parameter does not contain a full path and file name for the file, WritePrivateProfileString searches the Windows directory for the file. If the file does not exist, this function creates the file in the Windows directory.

If lpFileName contains a full path and file name and the file does not exist, WritePrivateProfileString creates the file. The specified directory must already exist.

The system keeps a cached version of the most recent registry file mapping to improve performance. If all parameters are NULL, the function flushes the cache. While the system is editing the cached version of the file, processes that edit the file itself will use the original file until the cache has been cleared.

The system maps most .ini file references to the registry, using the mapping defined under the following registry key:

HKEY_LOCAL_MACHINE
   SOFTWARE
      Microsoft
         Windows NT
            CurrentVersion
               IniFileMapping

This mapping is likely if an application modifies system-component initialization files, such as Control.ini, System.ini, and Winfile.ini. In this case, the function writes information to the registry, not to the initialization file; the change in the storage location has no effect on the function's behavior.

The profile functions use the following steps to locate initialization information:

1. Look in the registry for the name of the initialization file under the IniFileMapping key.
2. Look for the section name specified by lpAppName. This will be a named value under the key that has the name of the initialization file, or a subkey with this name, or the name will not exist as either a value or subkey.
3. If the section name specified by lpAppName is a named value, then that value specifies where in the registry you will find the keys for the section.
4. If the section name specified by lpAppName is a subkey, then named values under that subkey specify where in the registry you will find the keys for the section. If the key you are looking for does not exist as a named value, then there will be an unnamed value (shown as <No Name>) that specifies the default location in the registry where you will find the key.
5. If the section name specified by lpAppName does not exist as a named value or as a subkey, then there will be an unnamed value (shown as <No Name>) that specifies the default location in the registry where you will find the keys for the section.
6. If there is no subkey or entry for the section name, then look for the actual initialization file on the disk and read its contents.

When looking at values in the registry that specify other registry locations, there are several prefixes that change the behavior of the .ini file mapping:

• ! - this character forces all writes to go both to the registry and to the .ini file on disk.
• # - this character causes the registry value to be set to the value in the Windows 3.1 .ini file when a new user logs in for the first time after setup.
• @ - this character prevents any reads from going to the .ini file on disk if the requested data is not found in the registry.
• USR: - this prefix stands for HKEY_CURRENT_USER, and the text after the prefix is relative to that key.
• SYS: - this prefix stands for HKEY_LOCAL_MACHINE\SOFTWARE, and the text after the prefix is relative to that key.

An application using the WritePrivateProfileString function to enter .ini file information into the registry should follow these guidelines:

• Ensure that no .ini file of the specified name exists on the system.
• Ensure that there is a key entry in the registry that specifies the .ini file. This entry should be under the path HKEY_LOCAL_MACHINE\SOFTWARE \Microsoft\Windows NT\CurrentVersion\IniFileMapping.
• Specify a value for that .ini file key entry that specifies a section. That is to say, an application must specify a section name, as it would appear within an .ini file or registry entry. Here is an example: [My Section].
• For system files, specify SYS for an added value.
• For application files, specify USR within the added value. Here is an example: "My Section: USR: App Name\Section". And, since USR indicates a mapping under HKEY_CURRENT_USER, the application should also create a key under HKEY_CURRENT_USER that specifies the application name listed in the added value. For the example just given, that would be "App Name".
• After following the preceding steps, an application setup program should call WritePrivateProfileString with the first three parameters set to NULL, and the fourth parameter set to the INI file name. For example:

  WritePrivateProfileString( NULL, NULL, NULL, L"appname.ini" );

• Such a call causes the mapping of an .ini file to the registry to take effect before the next system reboot. The system rereads the mapping information into shared memory. A user will not have to reboot their computer after installing an application in order to have future invocations of the application see the mapping of the .ini file to the registry.

The following sample code illustrates the preceding guidelines and is based on several assumptions:

• There is an application named App Name.
• That application uses an .ini file named AppName.ini.
• There is a section in the .ini file that we want to look like this:

  [Section1] 
    FirstKey = It all worked out okay. 
    SecondKey = By golly, it works. 
    ThirdKey = Another test.
  

• The user will not have to reboot the system in order to have future invocations of the application see the mapping of the .ini file to the registry.

#include <windows.h> 
#include <tchar.h>
#include <stdio.h> 
 
int main() 
{ 
   TCHAR   inBuf[80]; 
   HKEY   hKey1, hKey2; 
   DWORD  dwDisposition; 
   LONG   lRetCode; 
   TCHAR   szData[] = TEXT("USR:App Name\\Section1");
 
   // Create the .ini file key. 
   lRetCode = RegCreateKeyEx ( HKEY_LOCAL_MACHINE, 
       TEXT("SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\IniFileMapping\\appname.ini"), 
       0, 
       NULL, 
       REG_OPTION_NON_VOLATILE, 
       KEY_WRITE, 
       NULL, 
       &hKey1, 
       &dwDisposition); 
 
   if (lRetCode != ERROR_SUCCESS)
   { 
      printf ("Error in creating appname.ini key (%d).\n", lRetCode); 
      return (0) ; 
   } 
 
   // Set a section value 
   lRetCode = RegSetValueEx ( hKey1, 
                              TEXT("Section1"), 
                              0, 
                              REG_SZ, 
                              (BYTE *)szData, 
                              sizeof(szData)); 
 
   if (lRetCode != ERROR_SUCCESS) 
   { 
      printf ("Error in setting Section1 value\n"); 
      // Close the key
      lRetCode = RegCloseKey( hKey1 );
      if( lRetCode != ERROR_SUCCESS )
      {
         printf("Error in RegCloseKey (%d).\n", lRetCode);
         return (0) ; 
      }
   } 
 
   // Create an App Name key 
   lRetCode = RegCreateKeyEx ( HKEY_CURRENT_USER, 
                               TEXT("App Name"), 
                               0, 
                               NULL, 
                               REG_OPTION_NON_VOLATILE,
                               KEY_WRITE, 
                               NULL, 
                               &hKey2, 
                               &dwDisposition); 
 
   if (lRetCode != ERROR_SUCCESS) 
   { 
      printf ("Error in creating App Name key (%d).\n", lRetCode); 

      // Close the key
      lRetCode = RegCloseKey( hKey2 );
      if( lRetCode != ERROR_SUCCESS )
      {
         printf("Error in RegCloseKey (%d).\n", lRetCode);
         return (0) ; 
      }
   } 
 
   // Force the system to read the mapping into shared memory 
   // so that future invocations of the application will see it 
   // without the user having to reboot the system 
   WritePrivateProfileStringW( NULL, NULL, NULL, L"appname.ini" ); 
 
   // Write some added values 
   WritePrivateProfileString (TEXT("Section1"), 
                              TEXT("FirstKey"), 
                              TEXT("It all worked out OK."), 
                              TEXT("appname.ini")); 
   WritePrivateProfileString (TEXT("Section1"), 
                              TEXT("SecondKey"), 
                              TEXT("By golly, it works!"), 
                              TEXT("appname.ini")); 
   WritePrivateProfileString (TEXT("Section1"), 
                              TEXT("ThirdKey"), 
                              TEXT("Another test..."), 
                              TEXT("appname.ini")); 

   // Test 
   GetPrivateProfileString (TEXT("Section1"), 
                            TEXT("FirstKey"), 
                            TEXT("Error: GPPS failed"), 
                            inBuf, 
                            80, 
                            TEXT("appname.ini")); 
   _tprintf (TEXT("Key: %s\n"), inBuf); 
 
   // Close the keys
   lRetCode = RegCloseKey( hKey1 );
   if( lRetCode != ERROR_SUCCESS )
   {
      printf("Error in RegCloseKey (%d).\n", lRetCode);
      return(0);
   }

   lRetCode = RegCloseKey( hKey2 );
   if( lRetCode != ERROR_SUCCESS )
   {
      printf("Error in RegCloseKey (%d).\n", lRetCode);
      return(0);
   }
   
   return(1); 
}

GetPrivateProfileString

WriteProfileString