Record-locking should not be used in combination with the fopen(), fread(), fwrite(), and other stdio functions. Instead, the more primitive, non-buffered functions (such as open()) should be used. Unexpected results may occur in processes that do buffering in the user address space. The process may later read/write data which is/was locked. The stdio functions are the most common source of unexpected buffering.

Record-locking should not be used in combination with buffered standard I/O streams (see [xref to Section 2.5]). Instead, non-buffered I/O should be used. Unexpected results may occur in processes that do buffering in the user address space. The process may later read/write data which is/was locked. Functions that operate on standard I/O streams are the most common source of such buffering.