In various multi threaded C and C++ projects I've seen the -pthread
flag applied to both the compiling and linking stage while others don't use it at all and just pass -lpthread
to the linking stage.
Is there any danger not compiling and linking with the -pthread
flag - i.e. what does -pthread
actually do ? I'm primarily interested in Linux platforms.
Try:
gcc -dumpspecs | grep pthread
and look for anything that starts with %{pthread:
.
On my computer, this causes files to be compiled with -D_REENTRANT
, and linked with -lpthread
. On other platforms, this could differ. Use -pthread
for most portability.
Using _REENTRANT
, on GNU libc, changes the way some libc headers work. As a specific example, it makes errno
call a function returning a thread-local location.