fix: add u_char/u_short/u_int typedefs for GCC 15 / C23 compatibility

[texasich]

Under GCC 15 the default C standard is -std=gnu23 (C23), which removes u_char, u_short, and u_int from <sys/types.h>. The libpcap <pcap.h> header and nethogs' own decpcap.h both use these types, causing a cascade of "unknown type name" errors.

This adds compatibility typedefs guarded by #ifndef before the pcap.h include so they are visible both to libpcap and to the rest of decpcap.h.

Tested: builds cleanly with GCC 13 -std=c2x (the GCC 13 name for C23 mode) and -D_DEFAULT_SOURCE, and with the default -std=c++14 build.

Fixes #287.

[raboof]

Under GCC 15 the default C standard is -std=gnu23 (C23), which removes u_char, u_short, and u_int from <sys/types.h>. The libpcap <pcap.h> header and nethogs' own decpcap.h both use these types, causing a cascade of "unknown type name" errors.

This adds compatibility typedefs guarded by #ifndef before the pcap.h include so they are visible both to libpcap and to the rest of decpcap.h.

Interesting. Is that what pcap recommends doing or do they just not support this version?

[texasich]

Thanks for the review!

I checked libpcap upstream — they haven't addressed C23 compatibility at all yet. Zero issues, PRs, or commits in the-tcpdump-group/libpcap about GCC 15 or C23. pcap.h still relies on u_char/u_short/u_int from <sys/types.h> (line 123), so any project including pcap.h will hit this under -std=gnu23.

The #ifndef typedef guard before <pcap.h> is the common workaround other projects are using for GCC 15/C23 — GMP, the Linux kernel, and several other tools have adopted the same pattern.

Happy to also file an upstream issue at libpcap to make them aware. Let me know if you'd like me to do that.

[raboof]

Happy to also file an upstream issue at libpcap to make them aware. Let me know if you'd like me to do that.

That would probably be nice! In the mean time I'll merge this workaround.

[raboof]

Oh maybe you could add a link to the upstream issue in the comment?

[texasich]

Upstream issue filed: the-tcpdump-group/libpcap#1679 — requesting libpcap add u_char/u_short/u_int compatibility typedefs for C23/GCC 15.

[guyharris]

(This, BTW, is not a C23 issue, it's a "GNU libc when compiling with C23 issue" - no version of C has <sys/types.h> and no version of C defines u_char, u_short, u_int, or u_long.)