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🛠 Add basic array safety functions and backwards-compatible result ty…
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…pe (#3805)
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ThePhD authored Jan 16, 2024
1 parent 64091b7 commit 13ec66b
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Showing 2 changed files with 82 additions and 8 deletions.
44 changes: 38 additions & 6 deletions include/fmt/base.h
Original file line number Diff line number Diff line change
Expand Up @@ -276,6 +276,8 @@
# define FMT_UNICODE !FMT_MSC_VERSION
#endif

#define FMT_FWD(...) static_cast<decltype(__VA_ARGS__)&&>(__VA_ARGS__)

// Enable minimal optimizations for more compact code in debug mode.
FMT_GCC_PRAGMA("GCC push_options")
#if !defined(__OPTIMIZE__) && !defined(__CUDACC__)
Expand Down Expand Up @@ -2861,8 +2863,10 @@ inline auto runtime(string_view s) -> runtime_format_string<> { return {{s}}; }

/** Formats a string and writes the output to ``out``. */
template <typename OutputIt,
FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
auto vformat_to(OutputIt out, string_view fmt, format_args args) -> OutputIt {
FMT_ENABLE_IF(detail::is_output_iterator<remove_cvref_t<OutputIt>,
char>::value)>
auto vformat_to(OutputIt&& out, string_view fmt, format_args args)
-> remove_cvref_t<OutputIt> {
auto&& buf = detail::get_buffer<char>(out);
detail::vformat_to(buf, fmt, args, {});
return detail::get_iterator(buf, out);
Expand All @@ -2881,10 +2885,11 @@ auto vformat_to(OutputIt out, string_view fmt, format_args args) -> OutputIt {
\endrst
*/
template <typename OutputIt, typename... T,
FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char>::value)>
FMT_INLINE auto format_to(OutputIt out, format_string<T...> fmt, T&&... args)
-> OutputIt {
return vformat_to(out, fmt, fmt::make_format_args(args...));
FMT_ENABLE_IF(detail::is_output_iterator<remove_cvref_t<OutputIt>,
char>::value)>
FMT_INLINE auto format_to(OutputIt&& out, format_string<T...> fmt, T&&... args)
-> remove_cvref_t<OutputIt> {
return vformat_to(FMT_FWD(out), fmt, fmt::make_format_args(args...));
}

template <typename OutputIt> struct format_to_n_result {
Expand Down Expand Up @@ -2919,6 +2924,33 @@ FMT_INLINE auto format_to_n(OutputIt out, size_t n, format_string<T...> fmt,
return vformat_to_n(out, n, fmt, fmt::make_format_args(args...));
}

template <typename OutputIt, typename OutputSen = OutputIt>
struct format_to_result {
/** Iterator pointing to just after the last succesful write in the range. */
OutputIt out;
/** Sentinel indicating the end of the output range. */
OutputSen out_last;

FMT_CONSTEXPR operator OutputIt&() & noexcept { return out; }
FMT_CONSTEXPR operator const OutputIt&() const& noexcept { return out; }
FMT_CONSTEXPR operator OutputIt&&() && noexcept {
return static_cast<OutputIt&&>(out);
}
};

template <size_t Size>
auto vformat_to(char (&out)[Size], string_view fmt, format_args args)
-> format_to_result<char*> {
format_to_n_result<char*> result = vformat_to_n(out, Size, fmt, args);
return {result.out, out + Size};
}

template <size_t Size, typename... T>
FMT_INLINE auto format_to(char (&out)[Size], format_string<T...> fmt,
T&&... args) -> format_to_result<char*> {
return vformat_to(out, fmt, fmt::make_format_args(args...));
}

/** Returns the number of chars in the output of ``format(fmt, args...)``. */
template <typename... T>
FMT_NODISCARD FMT_INLINE auto formatted_size(format_string<T...> fmt,
Expand Down
46 changes: 44 additions & 2 deletions test/base-test.cc
Original file line number Diff line number Diff line change
Expand Up @@ -9,15 +9,16 @@
#include "test-assert.h"
// clang-format on

#include "fmt/base.h"

#include <climits> // INT_MAX
#include <cstring> // std::strlen
#include <functional> // std::equal_to
#include <iterator> // std::back_insert_iterator
#include <iterator> // std::back_insert_iterator, std::distance
#include <limits> // std::numeric_limits
#include <string> // std::string
#include <type_traits> // std::is_same

#include "fmt/base.h"
#include "gmock/gmock.h"

using fmt::string_view;
Expand Down Expand Up @@ -692,6 +693,47 @@ TEST(core_test, format_to) {
EXPECT_EQ(s, "42");
}

TEST(core_test, format_to_c_array) {
char buffer[4];
auto result = fmt::format_to(buffer, "{}", 12345);
EXPECT_EQ(4, std::distance(&buffer[0], result.out));
EXPECT_EQ(0, std::distance(result.out, result.out_last));
EXPECT_EQ(buffer + 4, result.out);
EXPECT_EQ("1234", fmt::string_view(buffer, 4));

result = fmt::format_to(buffer, "{:s}", "foobar");
EXPECT_EQ(4, std::distance(&buffer[0], result.out));
EXPECT_EQ(0, std::distance(result.out, result.out_last));
EXPECT_EQ(buffer + 4, result.out);
EXPECT_EQ("foob", fmt::string_view(buffer, 4));

buffer[0] = 'x';
buffer[1] = 'x';
buffer[2] = 'x';
buffer[3] = 'x';
result = fmt::format_to(buffer, "{}", 'A');
EXPECT_EQ(1, std::distance(&buffer[0], result.out));
EXPECT_EQ(3, std::distance(result.out, result.out_last));
EXPECT_EQ(buffer + 1, result.out);
EXPECT_EQ("Axxx", fmt::string_view(buffer, 4));

result = fmt::format_to(buffer, "{}{} ", 'B', 'C');
EXPECT_EQ(3, std::distance(&buffer[0], result.out));
EXPECT_EQ(1, std::distance(result.out, result.out_last));
EXPECT_EQ(buffer + 3, result.out);
EXPECT_EQ("BC x", fmt::string_view(buffer, 4));

result = fmt::format_to(buffer, "{}", "ABCDE");
EXPECT_EQ(4, std::distance(&buffer[0], result.out));
EXPECT_EQ(0, std::distance(result.out, result.out_last));
EXPECT_EQ("ABCD", fmt::string_view(buffer, 4));

result = fmt::format_to(buffer, "{}", std::string(1000, '*'));
EXPECT_EQ(4, std::distance(&buffer[0], result.out));
EXPECT_EQ(0, std::distance(result.out, result.out_last));
EXPECT_EQ("****", fmt::string_view(buffer, 4));
}

#ifdef __cpp_lib_byte
TEST(core_test, format_byte) {
auto s = std::string();
Expand Down

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