ALT Example cleanup code using POSIX's open/close functions for file descirptors: #include <fcntl.h> #include <unistd.h> void closep(void* ptr) { int* p = ptr; if (!p || *p == -1) return; close(*p); } #define return_fd(desc) return ({ auto t = desc; desc = -1; t; }) int f () { [[gnu::cleanup(closep)]] int fd = open("", 0, 0); if (fd < 0) return -1; // Safe since closep checks for < 0 bool failure = false; // ... if (failure) return -1; // ... return_fd(fd); // Again safe } int main () { return 0; }

ALT #include <fcntl.h> #include <unistd.h> #define return_fd(desc) return ({ auto t = desc; desc = -1; t; }) int f () { int fd = open("", 0, 0); if (fd < 0) return -1; // Safe since closep checks for < 0 #if STYLE_1 _Defer { if (fd != -1) { close(fd); } } #else _Defer if (fd != -1) close(fd); #endif bool failure = false; // ... if (failure) return -1; // ... return_fd(fd); // Again safe } int main () { return 0; }

ALT A picture showing the assembly output of the two previously-pictured programs side by side. The defer version clearly produces far less output, even under optimization level -O3 (full command line flags: -O3 -Wall -Werror -std=gnu2y -fdefer-ts).