strings.h

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/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#pragma once
 
#include <ctype.h>
 
#include <sstream>
#include <string>
#include <string_view>
#include <type_traits>
#include <utility>
#include <vector>
 
namespace android {
namespace base {
 
// Splits a string into a vector of strings.
//
// The string is split at each occurrence of a character in delimiters.
//
// The empty string is not a valid delimiter list.
std::vector<std::string> Split(const std::string& s,
                               const std::string& delimiters);
 
// Splits a string into a vector of string tokens.
//
// The string is split at each occurrence of a character in delimiters.
// Coalesce runs of delimiter bytes and ignore delimiter bytes at the start or
// end of string. In other words, return only nonempty string tokens.
// Use when you don't care about recovering the original string with Join().
//
// Example:
//   Tokenize(" foo  bar ", " ") => {"foo", "bar"}
//   Join(Tokenize("  foo  bar", " "), " ") => "foo bar"
//
// The empty string is not a valid delimiter list.
std::vector<std::string> Tokenize(const std::string& s, const std::string& delimiters);
 
namespace internal {
template <typename>
constexpr bool always_false_v = false;
}
 
template <typename T>
std::string Trim(T&& t) {
  std::string_view sv;
  std::string s;
  if constexpr (std::is_convertible_v<T, std::string_view>) {
    sv = std::forward<T>(t);
  } else if constexpr (std::is_convertible_v<T, std::string>) {
    // The previous version of this function allowed for types which are implicitly convertible
    // to std::string but not to std::string_view. For these types we go through std::string first
    // here in order to retain source compatibility.
    s = t;
    sv = s;
  } else {
    static_assert(internal::always_false_v<T>,
                  "Implicit conversion to std::string or std::string_view not possible");
  }
 
  // Skip initial whitespace.
  while (!sv.empty() && isspace(sv.front())) {
    sv.remove_prefix(1);
  }
 
  // Skip terminating whitespace.
  while (!sv.empty() && isspace(sv.back())) {
    sv.remove_suffix(1);
  }
 
  return std::string(sv);
}
 
// We instantiate the common cases in strings.cpp.
extern template std::string Trim(const char*&);
extern template std::string Trim(const char*&&);
extern template std::string Trim(const std::string&);
extern template std::string Trim(const std::string&&);
extern template std::string Trim(std::string_view&);
extern template std::string Trim(std::string_view&&);
 
// Joins a container of things into a single string, using the given separator.
template <typename ContainerT, typename SeparatorT>
std::string Join(const ContainerT& things, SeparatorT separator) {
  if (things.empty()) {
    return "";
  }
 
  std::ostringstream result;
  result << *things.begin();
  for (auto it = std::next(things.begin()); it != things.end(); ++it) {
    result << separator << *it;
  }
  return result.str();
}
 
// We instantiate the common cases in strings.cpp.
extern template std::string Join(const std::vector<std::string>&, char);
extern template std::string Join(const std::vector<const char*>&, char);
extern template std::string Join(const std::vector<std::string>&, const std::string&);
extern template std::string Join(const std::vector<const char*>&, const std::string&);
 
// Tests whether 's' starts with 'prefix'.
bool StartsWith(std::string_view s, std::string_view prefix);
bool StartsWith(std::string_view s, char prefix);
bool StartsWithIgnoreCase(std::string_view s, std::string_view prefix);
 
// Tests whether 's' ends with 'suffix'.
bool EndsWith(std::string_view s, std::string_view suffix);
bool EndsWith(std::string_view s, char suffix);
bool EndsWithIgnoreCase(std::string_view s, std::string_view suffix);
 
// Tests whether 'lhs' equals 'rhs', ignoring case.
bool EqualsIgnoreCase(std::string_view lhs, std::string_view rhs);
 
// Removes `prefix` from the start of the given string and returns true (if
// it was present), false otherwise.
inline bool ConsumePrefix(std::string_view* s, std::string_view prefix) {
  if (!StartsWith(*s, prefix)) return false;
  s->remove_prefix(prefix.size());
  return true;
}
 
// Removes `suffix` from the end of the given string and returns true (if
// it was present), false otherwise.
inline bool ConsumeSuffix(std::string_view* s, std::string_view suffix) {
  if (!EndsWith(*s, suffix)) return false;
  s->remove_suffix(suffix.size());
  return true;
}
 
// Replaces `from` with `to` in `s`, once if `all == false`, or as many times as
// there are matches if `all == true`.
[[nodiscard]] std::string StringReplace(std::string_view s, std::string_view from,
                                        std::string_view to, bool all);
 
// Converts an errno number to its error message string.
std::string ErrnoNumberAsString(int errnum);
 
}  // namespace base
}  // namespace android