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add support for positional arguments as width and precision specifiers (#4643)

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* make positional arguments work as width and precision specifiers with floating-point formats too

* fix test case failing ci tests
This commit is contained in:
Kareem Otoum
2026-01-04 16:39:02 -08:00
committed by GitHub
parent 46a45990fe
commit 6b018edfb9
2 changed files with 59 additions and 4 deletions
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include/fmt/printf.h
+30 -4
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@@ -357,8 +357,21 @@ auto parse_header(const Char*& it, const Char* end, format_specs& specs,
if (specs.width == -1) report_error("number is too big");
} else if (*it == '*') {
++it;
specs.width = static_cast<int>(
get_arg(-1).visit(detail::printf_width_handler(specs)));
// Check for positional width argument like *1$
if (it != end && *it >= '0' && *it <= '9') {
int width_index = parse_nonnegative_int(it, end, -1);
if (it != end && *it == '$') {
++it;
specs.width = static_cast<int>(
get_arg(width_index).visit(detail::printf_width_handler(specs)));
} else {
// Invalid format, rewind and treat as non-positional
report_error("invalid format specifier");
}
} else {
specs.width = static_cast<int>(
get_arg(-1).visit(detail::printf_width_handler(specs)));
}
}
}
return arg_index;
@@ -439,8 +452,21 @@ void vprintf(buffer<Char>& buf, basic_string_view<Char> format,
specs.precision = parse_nonnegative_int(it, end, 0);
} else if (c == '*') {
++it;
specs.precision =
static_cast<int>(get_arg(-1).visit(printf_precision_handler()));
// Check for positional precision argument like .*1$
if (it != end && *it >= '0' && *it <= '9') {
int precision_index = parse_nonnegative_int(it, end, -1);
if (it != end && *it == '$') {
++it;
specs.precision = static_cast<int>(
get_arg(precision_index).visit(printf_precision_handler()));
} else {
// Invalid format, rewind and treat as non-positional
report_error("invalid format specifier");
}
} else {
specs.precision =
static_cast<int>(get_arg(-1).visit(printf_precision_handler()));
}
} else {
specs.precision = 0;
}