WritePrivateProfileString

WritePrivateProfileString is a Windows API function used to write data to INI-format configuration files. It is part of the Windows API and is implemented in Kernel32.dll. There are two variants: WritePrivateProfileStringA for ANSI and WritePrivateProfileStringW for Unicode.

The function writes the string specified by lpString to the key named by lpKeyName in the section named by lpAppName within the INI file identified by lpFileName. When used to write a value, all four parameters are provided with meaningful, non-null values. The function also supports deletion operations: if lpString is NULL, the specified key is deleted; if lpKeyName is NULL, the entire section is deleted; and if both lpAppName and lpKeyName are NULL with lpString NULL, the INI file can be deleted. The exact behavior depends on which parameters are NULL, following the documented combinations for writing or deleting keys, sections, or the whole file.

INI files used by this function are plain text files containing sections in brackets, and key-value pairs in the form Key=Value. The function returns a nonzero value on success and zero on failure, with error details obtainable via standard Win32 error reporting.

Usage notes: WritePrivateProfileString is a legacy API commonly found in older Windows applications. Modern Windows development often favors the registry or other configuration mechanisms, as INI-file handling is less robust and lacks built-in synchronization. When using this function, applications should ensure the INI file path is accessible to the running process and handle potential synchronization issues if multiple processes may modify the file concurrently.

See also GetPrivateProfileString, GetPrivateProfileSection, and related Get/WritePrivateProfileString APIs.