Re: portability of fopen and 'e' (O_CLOEXEC) flag

[Bruno Haible]

Hi Tim,

> i would like to ask for your expert knowledge.
> 
> How to prevent file descriptor leaks in a multi-threaded application
> that fork+exec. Quick answer is surely "use O_CLOEXEC" to close those
> file descriptors on exec.
> 
> But how does this work with fopen in a portable way ?
> GNU libc has the 'e' flag for exactly this.

Yes [1].

> How about other non-GNU OSes / alternative C libraries ?

POSIX [2][3], macOS [4], FreeBSD [5], Solaris [6] don't support this 'e' flag.

How about using open() with O_CLOEXEC, and then fdopen()?

Bruno

[1] http://man7.org/linux/man-pages/man3/fopen.3.html
[2] https://pubs.opengroup.org/onlinepubs/9699919799/functions/fopen.html
[3] http://man7.org/linux/man-pages/man3/fopen.3p.html
[4] 
https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/fopen.3.html
[5] 
https://www.freebsd.org/cgi/man.cgi?query=fopen&sektion=3&apropos=0&manpath=freebsd
[6] https://docs.oracle.com/cd/E36784_01/html/E36874/fopen-3c.html