base/strings/stringprintf.h

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_STRINGS_STRINGPRINTF_H_
#define BASE_STRINGS_STRINGPRINTF_H_

#include <stdarg.h>  // va_list

#include <string>
#include <string_view>

#include "base/base_export.h"
#include "base/check.h"
#include "base/compiler_specific.h"
#include "third_party/abseil-cpp/absl/strings/str_format.h"

namespace base {

// Returns a C++ string given `printf()`-like input. The format string must be a
// compile-time constant (like with `std::format()`), or this will not compile.
// TODO(crbug.com/40241565): Replace calls to this with direct calls to
// `absl::StrFormat()` and remove.
template <typename... Args>
[[nodiscard]] std::string StringPrintf(const absl::FormatSpec<Args...>& format,
                                       const Args&... args) {
  return absl::StrFormat(format, args...);
}
// Returns a C++ string given `printf()`-like input. The format string must be a
// run-time value (like with `std::vformat()`), or this will not compile.
// Because this does not check arguments at compile-time, prefer
// `StringPrintf()` whenever possible.
template <typename... Args>
[[nodiscard]] std::string StringPrintfNonConstexpr(std::string_view format,
                                                   const Args&... args) {
  std::string output;
  CHECK(absl::FormatUntyped(&output, absl::UntypedFormatSpec(format),
                            {absl::FormatArg(args)...}));
  return output;
}

// If possible, guide users to use `StringPrintf()` instead of
// `StringPrintfNonConstexpr()` when the format string is constexpr.
//
// It would be nice to do this with `std::enable_if`, but I don't know of a way;
// whether a string constant's value is available at compile time is not
// something easily obtained from the type system, and trying to pass various
// forms of string constant to non-type template parameters produces a variety
// of compile errors.
#if HAS_ATTRIBUTE(enable_if)
// Disable calling with a constexpr `std::string_view`.
template <typename... Args>
[[nodiscard]] std::string StringPrintfNonConstexpr(std::string_view format,
                                                   const Args&... args)
    ENABLE_IF_ATTR(
        [](std::string_view s) { return s.empty() || s[0] == s[0]; }(format),
        "Use StringPrintf() for constexpr format strings") = delete;
// Disable calling with a constexpr `char[]` or `char*`.
template <typename... Args>
[[nodiscard]] std::string StringPrintfNonConstexpr(const char* format,
                                                   const Args&... args)
    ENABLE_IF_ATTR([](const char* s) { return !!s; }(format),
                   "Use StringPrintf() for constexpr format strings") = delete;
#endif

// Returns a C++ string given `vprintf()`-like input.
[[nodiscard]] PRINTF_FORMAT(1, 0) BASE_EXPORT std::string
    StringPrintV(const char* format, va_list ap);

// Like `StringPrintf()`, but appends result to a supplied string.
// TODO(crbug.com/40241565): Replace calls to this with direct calls to
// `absl::StrAppendFormat()` and remove.
template <typename... Args>
void StringAppendF(std::string* dst,
                   const absl::FormatSpec<Args...>& format,
                   const Args&... args) {
  absl::StrAppendFormat(dst, format, args...);
}

// Like `StringPrintV()`, but appends result to a supplied string.
PRINTF_FORMAT(2, 0)
BASE_EXPORT
void StringAppendV(std::string* dst, const char* format, va_list ap);

}  // namespace base

#endif  // BASE_STRINGS_STRINGPRINTF_H_