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- [libc] scanf: do not count suppressed conversions in the return value
- scanf_main() incremented the result for every successful conversion except %n,
- including assignment-suppressed ones ("%*d") and "%%". C requires the number of
- input items *assigned*. Example: sscanf("12 34", "%*d%d", &x) returned 2
- instead of 1; sscanf("420jpeg", "%*d%*[pP]%d", &x) returned 1 without writing x
- (breaks x264's y4m colorspace/bit depth parsing). Still present in llvm main
- as of 2026-10.
- diff --git a/libc/src/stdio/scanf_core/scanf_main.h b/libc/src/stdio/scanf_core/scanf_main.h
- index f975d85..e1eb5fb 100644
- --- a/libc/src/stdio/scanf_core/scanf_main.h
- +++ b/libc/src/stdio/scanf_core/scanf_main.h
- @@ -32,9 +32,10 @@ int scanf_main(Reader<T> *reader, const char *__restrict str,
- cur_section = parser.get_next_section()) {
- if (cur_section.has_conv) {
- ret_val = convert(reader, cur_section);
- - // The %n (current position) conversion doesn't increment the number of
- - // assignments.
- - if (cur_section.conv_name != 'n')
- + // Only assigned items count: not %n (current position), not %% and not
- + // conversions with assignment suppression ('*', the NO_WRITE flag).
- + if (cur_section.conv_name != 'n' && cur_section.conv_name != '%' &&
- + (cur_section.flags & FormatFlags::NO_WRITE) == 0)
- conversions += ret_val == READ_OK ? 1 : 0;
- } else {
- ret_val = raw_match(reader, cur_section.raw_string);
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