SPNU151W January 1998 – March 2023 66AK2E05 , 66AK2H06 , 66AK2H12 , 66AK2H14 , AM1705 , AM1707 , AM1802 , AM1806 , AM1808 , AM1810 , AM5K2E04 , OMAP-L132 , OMAP-L137 , OMAP-L138 , SM470R1B1M-HT , TMS470R1A288 , TMS470R1A384 , TMS470R1A64 , TMS470R1B1M , TMS470R1B512 , TMS470R1B768
The once pragma tells the C preprocessor to ignore a #include directive if that header file has already been included. For example, this pragma may be used if header files contain definitions, such as struct definitions, that would cause a compilation error if they were executed more than once.
This pragma should be used at the beginning of a header file that should only be included once. For example:
// hdr.h
#pragma once
#warn You will only see this message one time
struct foo
{
int member;
};This pragma is not part of the C or C++ standard, but it is a widely-supported preprocessor directive. Note that this pragma does not protect against the inclusion of a header file with the same contents that has been copied to another directory.