Why are these not compiler errors by default? Opting in to such important safety features seems like broken design.
Also, in personal projects, I almost always used custom wrapper functions for printf/fprintf/sprintf for various reasons, so that default wouldn’t be of much use, unless maybe I could enable it for the custom functions.
For loading translated strings, I'm missing some library function to verify whether two format strings are argument-compatible.
Aren't those usually resolved to string literals by preprocessor such that the compiler still could emit a warning?
(I have no recommendations. When I've seen this stuff done properly, on the occasions I've managed not to avoid doing it, it's always been using some in-house system.)
You can with the $ syntax. Never seen it used though. Maybe it isn't very portable.
I think the real reason you rarely see it, is it is only used with internationalisation–the idea being if you translate the format string, the translator may need to reorder the parameters for a natural translation, given differences in word order in different languages. However, a lot of software isn't internationalised, or if it is, the internationalisation is in end-user facing text, which nowadays usually ends up in a GUI or web UI, so printf has less to do with it. And the kind of lower-level tools/components for which people still often use C are less likely to be internationalised, since they are targeted at a technical audience who are expected to be able to read some level of English.
I like printf format strings, but as a way of handling localizable strings I don't think they are the best.
A good example of this is pluralisation. We've all done things like:
printf("%d file(s) copied\n", count);
printf("%d file%s copied\n", count, count != 1 ? "s" : "");
printf() has zero hope of coping with this complexity. gettext provides a special function to handle this, ngettext(), which is passed the number as a separate argument, so it can select which plural form to use. And then the translated message files contain a header defining how many plural forms that language has, and the rules to choose which one to use. And for some languages it is crazy complex. Arabic is the most extreme, for which the manual gives this plural rule:
Plural-Forms: nplurals=6; \
plural=n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 \
: n%100>=11 ? 4 : 5;One practical reason I can think of is because not everyone compiles their own code.
You must most definitely look for and enable such flags as they become available in your own projects. (eg I was rooting for -Wlifetime but it did not land for various reasons)
But when you compile other people's code, your breaking your local build doesn't help anyone. Best you can do is to submit a bug report, which may or may not be ignored.
> The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh, cos, exit, exp, fabs, floor, fmod, fprintf, fputs, free, frexp, fscanf, isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, tolower, toupper, labs, ldexp, log10, log, malloc, memchr, memcmp, memcpy, memset, modf, pow, printf, putchar, puts, realloc, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk, strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized as built-in functions unless -fno-builtin is specified (or -fno-builtin-function is specified for an individual function).
Builtin here doesn't mean that GCC won't ever emit calls to library functions, only that it reserves not to and allows itselfs to make assumptions about how the functions work, including diagnosing misuse.
The library functions themselves might also be marked with __attribute__(format(...)) as the sibling comment notes but that is not necessarily required for GCC to check the format strings.