> whether they get a given error code or not. Helpfully, the Emacs code is commented, which helps explain the pattern: if (errno = ack.hf_retcode) /* set

> whether they get a given error code or not. Helpfully, the Emacs code is commented, which helps explain the pattern: if (errno = ack.hf_retcode) /* set errno based on returned */ return (-1); /* code, if 0, then no error */ Presumably errno is a global, and when it is set to a value other than zero, the function returns. So, it isn't an example of = being used in place of ==, at least this snippet appears to be correct.