Often one can ignore the errno case, as the input is (by then) semi-constrained, and its ambiguity resolution is not needed. e.g. so an idomatic pattern from s

Often one can ignore the errno case, as the input is (by then) semi-constrained, and its ambiguity resolution is not needed. e.g. so an idomatic pattern from some real code would be something like: static bool parse_thing (char *value, struct thing *th) { char *endp = NULL; unsigned long firstport = strtoul(value, &endp, 10); if (endp == value || *endp || firstport > 0xffff) { /* Do something with error, like log it */ return false; } th->firstport = firstport; return true; } But granted, for the general case I'd prefer to use some helper like either of: bool parse_decimal_uint32(struct string const *str, uint32_t *outval); bool parse_decimal_uint32(char const *str, unsigned slen, uint32_t *outval);