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// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This file defines utility functions for working with strings.
#include <ctype.h>
#include <stdarg.h> // va_list
#include <initializer_list>
#include <string>
#include <vector>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/strings/string16.h"
#include "base/strings/string_piece.h" // For implicit conversions.
#include "build/build_config.h"
namespace base {
// C standard-library functions that aren't cross-platform are provided as
// "base::...", and their prototypes are listed below. These functions are
// then implemented as inline calls to the platform-specific equivalents in the
// platform-specific headers.
// Wrapper for vsnprintf that always null-terminates and always returns the
// number of characters that would be in an untruncated formatted
// string, even when truncation occurs.
int vsnprintf(char* buffer, size_t size, const char* format, va_list arguments)
// Some of these implementations need to be inlined.
// We separate the declaration from the implementation of this inline
// function just so the PRINTF_FORMAT works.
inline int snprintf(char* buffer,
size_t size,
_Printf_format_string_ const char* format,
...) PRINTF_FORMAT(3, 4);
inline int snprintf(char* buffer,
size_t size,
_Printf_format_string_ const char* format,
...) {
va_list arguments;
va_start(arguments, format);
int result = vsnprintf(buffer, size, format, arguments);
return result;
// BSD-style safe and consistent string copy functions.
// Copies |src| to |dst|, where |dst_size| is the total allocated size of |dst|.
// Copies at most |dst_size|-1 characters, and always NULL terminates |dst|, as
// long as |dst_size| is not 0. Returns the length of |src| in characters.
// If the return value is >= dst_size, then the output was truncated.
// NOTE: All sizes are in number of characters, NOT in bytes.
BASE_EXPORT size_t strlcpy(char* dst, const char* src, size_t dst_size);
BASE_EXPORT size_t wcslcpy(wchar_t* dst, const wchar_t* src, size_t dst_size);
// Scan a wprintf format string to determine whether it's portable across a
// variety of systems. This function only checks that the conversion
// specifiers used by the format string are supported and have the same meaning
// on a variety of systems. It doesn't check for other errors that might occur
// within a format string.
// Nonportable conversion specifiers for wprintf are:
// - 's' and 'c' without an 'l' length modifier. %s and %c operate on char
// data on all systems except Windows, which treat them as wchar_t data.
// Use %ls and %lc for wchar_t data instead.
// - 'S' and 'C', which operate on wchar_t data on all systems except Windows,
// which treat them as char data. Use %ls and %lc for wchar_t data
// instead.
// - 'F', which is not identified by Windows wprintf documentation.
// - 'D', 'O', and 'U', which are deprecated and not available on all systems.
// Use %ld, %lo, and %lu instead.
// Note that there is no portable conversion specifier for char data when
// working with wprintf.
// This function is intended to be called from base::vswprintf.
BASE_EXPORT bool IsWprintfFormatPortable(const wchar_t* format);
// ASCII-specific tolower. The standard library's tolower is locale sensitive,
// so we don't want to use it here.
inline char ToLowerASCII(char c) {
return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c;
inline char16 ToLowerASCII(char16 c) {
return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c;
// ASCII-specific toupper. The standard library's toupper is locale sensitive,
// so we don't want to use it here.
inline char ToUpperASCII(char c) {
return (c >= 'a' && c <= 'z') ? (c + ('A' - 'a')) : c;
inline char16 ToUpperASCII(char16 c) {
return (c >= 'a' && c <= 'z') ? (c + ('A' - 'a')) : c;
// Converts the given string to it's ASCII-lowercase equivalent.
BASE_EXPORT std::string ToLowerASCII(StringPiece str);
BASE_EXPORT string16 ToLowerASCII(StringPiece16 str);
// Converts the given string to it's ASCII-uppercase equivalent.
BASE_EXPORT std::string ToUpperASCII(StringPiece str);
BASE_EXPORT string16 ToUpperASCII(StringPiece16 str);
// Functor for case-insensitive ASCII comparisons for STL algorithms like
// std::search.
// Note that a full Unicode version of this functor is not possible to write
// because case mappings might change the number of characters, depend on
// context (combining accents), and require handling UTF-16. If you need
// proper Unicode support, use base::i18n::ToLower/FoldCase and then just
// use a normal operator== on the result.
template<typename Char> struct CaseInsensitiveCompareASCII {
bool operator()(Char x, Char y) const {
return ToLowerASCII(x) == ToLowerASCII(y);
// Like strcasecmp for case-insensitive ASCII characters only. Returns:
// -1 (a < b)
// 0 (a == b)
// 1 (a > b)
// (unlike strcasecmp which can return values greater or less than 1/-1). For
// full Unicode support, use base::i18n::ToLower or base::i18h::FoldCase
// and then just call the normal string operators on the result.
BASE_EXPORT int CompareCaseInsensitiveASCII(StringPiece a, StringPiece b);
BASE_EXPORT int CompareCaseInsensitiveASCII(StringPiece16 a, StringPiece16 b);
// Equality for ASCII case-insensitive comparisons. For full Unicode support,
// use base::i18n::ToLower or base::i18h::FoldCase and then compare with either
// == or !=.
BASE_EXPORT bool EqualsCaseInsensitiveASCII(StringPiece a, StringPiece b);
BASE_EXPORT bool EqualsCaseInsensitiveASCII(StringPiece16 a, StringPiece16 b);
// These threadsafe functions return references to globally unique empty
// strings.
// It is likely faster to construct a new empty string object (just a few
// instructions to set the length to 0) than to get the empty string instance
// returned by these functions (which requires threadsafe static access).
// CONSTRUCTORS. There is only one case where you should use these: functions
// which need to return a string by reference (e.g. as a class member
// accessor), and don't have an empty string to use (e.g. in an error case).
// These should not be used as initializers, function arguments, or return
// values for functions which return by value or outparam.
BASE_EXPORT const std::string& EmptyString();
BASE_EXPORT const string16& EmptyString16();
// Contains the set of characters representing whitespace in the corresponding
// encoding. Null-terminated. The ASCII versions are the whitespaces as defined
// by HTML5, and don't include control characters.
BASE_EXPORT extern const wchar_t kWhitespaceWide[]; // Includes Unicode.
BASE_EXPORT extern const char16 kWhitespaceUTF16[]; // Includes Unicode.
BASE_EXPORT extern const char kWhitespaceASCII[];
BASE_EXPORT extern const char16 kWhitespaceASCIIAs16[]; // No unicode.
// Null-terminated string representing the UTF-8 byte order mark.
BASE_EXPORT extern const char kUtf8ByteOrderMark[];
// Removes characters in |remove_chars| from anywhere in |input|. Returns true
// if any characters were removed. |remove_chars| must be null-terminated.
// NOTE: Safe to use the same variable for both |input| and |output|.
BASE_EXPORT bool RemoveChars(const string16& input,
StringPiece16 remove_chars,
string16* output);
BASE_EXPORT bool RemoveChars(const std::string& input,
StringPiece remove_chars,
std::string* output);
// Replaces characters in |replace_chars| from anywhere in |input| with
// |replace_with|. Each character in |replace_chars| will be replaced with
// the |replace_with| string. Returns true if any characters were replaced.
// |replace_chars| must be null-terminated.
// NOTE: Safe to use the same variable for both |input| and |output|.
BASE_EXPORT bool ReplaceChars(const string16& input,
StringPiece16 replace_chars,
const string16& replace_with,
string16* output);
BASE_EXPORT bool ReplaceChars(const std::string& input,
StringPiece replace_chars,
const std::string& replace_with,
std::string* output);
enum TrimPositions {
TRIM_LEADING = 1 << 0,
// Removes characters in |trim_chars| from the beginning and end of |input|.
// The 8-bit version only works on 8-bit characters, not UTF-8. Returns true if
// any characters were removed.
// It is safe to use the same variable for both |input| and |output| (this is
// the normal usage to trim in-place).
BASE_EXPORT bool TrimString(const string16& input,
StringPiece16 trim_chars,
string16* output);
BASE_EXPORT bool TrimString(const std::string& input,
StringPiece trim_chars,
std::string* output);
// StringPiece versions of the above. The returned pieces refer to the original
// buffer.
BASE_EXPORT StringPiece16 TrimString(StringPiece16 input,
StringPiece16 trim_chars,
TrimPositions positions);
BASE_EXPORT StringPiece TrimString(StringPiece input,
StringPiece trim_chars,
TrimPositions positions);
// Truncates a string to the nearest UTF-8 character that will leave
// the string less than or equal to the specified byte size.
BASE_EXPORT void TruncateUTF8ToByteSize(const std::string& input,
const size_t byte_size,
std::string* output);
// Trims any whitespace from either end of the input string.
// The StringPiece versions return a substring referencing the input buffer.
// The ASCII versions look only for ASCII whitespace.
// The std::string versions return where whitespace was found.
// NOTE: Safe to use the same variable for both input and output.
BASE_EXPORT TrimPositions TrimWhitespace(const string16& input,
TrimPositions positions,
string16* output);
BASE_EXPORT StringPiece16 TrimWhitespace(StringPiece16 input,
TrimPositions positions);
BASE_EXPORT TrimPositions TrimWhitespaceASCII(const std::string& input,
TrimPositions positions,
std::string* output);
BASE_EXPORT StringPiece TrimWhitespaceASCII(StringPiece input,
TrimPositions positions);
// Searches for CR or LF characters. Removes all contiguous whitespace
// strings that contain them. This is useful when trying to deal with text
// copied from terminals.
// Returns |text|, with the following three transformations:
// (1) Leading and trailing whitespace is trimmed.
// (2) If |trim_sequences_with_line_breaks| is true, any other whitespace
// sequences containing a CR or LF are trimmed.
// (3) All other whitespace sequences are converted to single spaces.
BASE_EXPORT string16 CollapseWhitespace(
const string16& text,
bool trim_sequences_with_line_breaks);
BASE_EXPORT std::string CollapseWhitespaceASCII(
const std::string& text,
bool trim_sequences_with_line_breaks);
// Returns true if |input| is empty or contains only characters found in
// |characters|.
BASE_EXPORT bool ContainsOnlyChars(StringPiece input, StringPiece characters);
BASE_EXPORT bool ContainsOnlyChars(StringPiece16 input,
StringPiece16 characters);
// Returns true if the specified string matches the criteria. How can a wide
// string be 8-bit or UTF8? It contains only characters that are < 256 (in the
// first case) or characters that use only 8-bits and whose 8-bit
// representation looks like a UTF-8 string (the second case).
// Note that IsStringUTF8 checks not only if the input is structurally
// valid but also if it doesn't contain any non-character codepoint
// (e.g. U+FFFE). It's done on purpose because all the existing callers want
// to have the maximum 'discriminating' power from other encodings. If
// there's a use case for just checking the structural validity, we have to
// add a new function for that.
// IsStringASCII assumes the input is likely all ASCII, and does not leave early
// if it is not the case.
BASE_EXPORT bool IsStringUTF8(StringPiece str);
BASE_EXPORT bool IsStringASCII(StringPiece str);
BASE_EXPORT bool IsStringASCII(StringPiece16 str);
#if defined(WCHAR_T_IS_UTF32)
BASE_EXPORT bool IsStringASCII(WStringPiece str);
// Compare the lower-case form of the given string against the given
// previously-lower-cased ASCII string (typically a constant).
#if defined(STARBOARD)
// TODO[Cobalt]: deprecate this function and use the other two instead.
BASE_EXPORT bool LowerCaseEqualsASCII(const char* a_begin,
const char* a_end,
const char* b);
BASE_EXPORT bool LowerCaseEqualsASCII(StringPiece str,
StringPiece lowecase_ascii);
BASE_EXPORT bool LowerCaseEqualsASCII(StringPiece16 str,
StringPiece lowecase_ascii);
// Performs a case-sensitive string compare of the given 16-bit string against
// the given 8-bit ASCII string (typically a constant). The behavior is
// undefined if the |ascii| string is not ASCII.
BASE_EXPORT bool EqualsASCII(StringPiece16 str, StringPiece ascii);
// Indicates case sensitivity of comparisons. Only ASCII case insensitivity
// is supported. Full Unicode case-insensitive conversions would need to go in
// base/i18n so it can use ICU.
// If you need to do Unicode-aware case-insensitive StartsWith/EndsWith, it's
// best to call base::i18n::ToLower() or base::i18n::FoldCase() (see
// base/i18n/case_conversion.h for usage advice) on the arguments, and then use
// the results to a case-sensitive comparison.
enum class CompareCase {
BASE_EXPORT bool StartsWith(StringPiece str,
StringPiece search_for,
CompareCase case_sensitivity);
BASE_EXPORT bool StartsWith(StringPiece16 str,
StringPiece16 search_for,
CompareCase case_sensitivity);
BASE_EXPORT bool EndsWith(StringPiece str,
StringPiece search_for,
CompareCase case_sensitivity);
BASE_EXPORT bool EndsWith(StringPiece16 str,
StringPiece16 search_for,
CompareCase case_sensitivity);
// Determines the type of ASCII character, independent of locale (the C
// library versions will change based on locale).
template <typename Char>
inline bool IsAsciiWhitespace(Char c) {
return c == ' ' || c == '\r' || c == '\n' || c == '\t';
template <typename Char>
inline bool IsAsciiAlpha(Char c) {
return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
template <typename Char>
inline bool IsAsciiUpper(Char c) {
return c >= 'A' && c <= 'Z';
template <typename Char>
inline bool IsAsciiLower(Char c) {
return c >= 'a' && c <= 'z';
template <typename Char>
inline bool IsAsciiDigit(Char c) {
return c >= '0' && c <= '9';
template <typename Char>
inline bool IsHexDigit(Char c) {
return (c >= '0' && c <= '9') ||
(c >= 'A' && c <= 'F') ||
(c >= 'a' && c <= 'f');
// Returns the integer corresponding to the given hex character. For example:
// '4' -> 4
// 'a' -> 10
// 'B' -> 11
// Assumes the input is a valid hex character. DCHECKs in debug builds if not.
BASE_EXPORT char HexDigitToInt(wchar_t c);
// Returns true if it's a Unicode whitespace character.
BASE_EXPORT bool IsUnicodeWhitespace(wchar_t c);
// Return a byte string in human-readable format with a unit suffix. Not
// appropriate for use in any UI; use of FormatBytes and friends in ui/base is
// highly recommended instead. TODO(avi): Figure out how to get callers to use
// FormatBytes instead; remove this.
BASE_EXPORT string16 FormatBytesUnlocalized(int64_t bytes);
// Starting at |start_offset| (usually 0), replace the first instance of
// |find_this| with |replace_with|.
BASE_EXPORT void ReplaceFirstSubstringAfterOffset(
base::string16* str,
size_t start_offset,
StringPiece16 find_this,
StringPiece16 replace_with);
BASE_EXPORT void ReplaceFirstSubstringAfterOffset(
std::string* str,
size_t start_offset,
StringPiece find_this,
StringPiece replace_with);
// Starting at |start_offset| (usually 0), look through |str| and replace all
// instances of |find_this| with |replace_with|.
// This does entire substrings; use std::replace in <algorithm> for single
// characters, for example:
// std::replace(str.begin(), str.end(), 'a', 'b');
BASE_EXPORT void ReplaceSubstringsAfterOffset(
string16* str,
size_t start_offset,
StringPiece16 find_this,
StringPiece16 replace_with);
BASE_EXPORT void ReplaceSubstringsAfterOffset(
std::string* str,
size_t start_offset,
StringPiece find_this,
StringPiece replace_with);
// Reserves enough memory in |str| to accommodate |length_with_null| characters,
// sets the size of |str| to |length_with_null - 1| characters, and returns a
// pointer to the underlying contiguous array of characters. This is typically
// used when calling a function that writes results into a character array, but
// the caller wants the data to be managed by a string-like object. It is
// convenient in that is can be used inline in the call, and fast in that it
// avoids copying the results of the call from a char* into a string.
// |length_with_null| must be at least 2, since otherwise the underlying string
// would have size 0, and trying to access &((*str)[0]) in that case can result
// in a number of problems.
// Internally, this takes linear time because the resize() call 0-fills the
// underlying array for potentially all
// (|length_with_null - 1| * sizeof(string_type::value_type)) bytes. Ideally we
// could avoid this aspect of the resize() call, as we expect the caller to
// immediately write over this memory, but there is no other way to set the size
// of the string, and not doing that will mean people who access |str| rather
// than str.c_str() will get back a string of whatever size |str| had on entry
// to this function (probably 0).
BASE_EXPORT char* WriteInto(std::string* str, size_t length_with_null);
BASE_EXPORT char16* WriteInto(string16* str, size_t length_with_null);
// Does the opposite of SplitString()/SplitStringPiece(). Joins a vector or list
// of strings into a single string, inserting |separator| (which may be empty)
// in between all elements.
// If possible, callers should build a vector of StringPieces and use the
// StringPiece variant, so that they do not create unnecessary copies of
// strings. For example, instead of using SplitString, modifying the vector,
// then using JoinString, use SplitStringPiece followed by JoinString so that no
// copies of those strings are created until the final join operation.
// Use StrCat (in base/strings/strcat.h) if you don't need a separator.
BASE_EXPORT std::string JoinString(const std::vector<std::string>& parts,
StringPiece separator);
BASE_EXPORT string16 JoinString(const std::vector<string16>& parts,
StringPiece16 separator);
BASE_EXPORT std::string JoinString(const std::vector<StringPiece>& parts,
StringPiece separator);
BASE_EXPORT string16 JoinString(const std::vector<StringPiece16>& parts,
StringPiece16 separator);
// Explicit initializer_list overloads are required to break ambiguity when used
// with a literal initializer list (otherwise the compiler would not be able to
// decide between the string and StringPiece overloads).
BASE_EXPORT std::string JoinString(std::initializer_list<StringPiece> parts,
StringPiece separator);
BASE_EXPORT string16 JoinString(std::initializer_list<StringPiece16> parts,
StringPiece16 separator);
// Replace $1-$2-$3..$9 in the format string with values from |subst|.
// Additionally, any number of consecutive '$' characters is replaced by that
// number less one. Eg $$->$, $$$->$$, etc. The offsets parameter here can be
// NULL. This only allows you to use up to nine replacements.
BASE_EXPORT string16 ReplaceStringPlaceholders(
const string16& format_string,
const std::vector<string16>& subst,
std::vector<size_t>* offsets);
BASE_EXPORT std::string ReplaceStringPlaceholders(
StringPiece format_string,
const std::vector<std::string>& subst,
std::vector<size_t>* offsets);
// Single-string shortcut for ReplaceStringHolders. |offset| may be NULL.
BASE_EXPORT string16 ReplaceStringPlaceholders(const string16& format_string,
const string16& a,
size_t* offset);
} // namespace base
#if defined(STARBOARD)
#include "base/strings/string_util_starboard.h"
#if defined(OS_WIN)
#include "base/strings/string_util_win.h"
#elif defined(OS_POSIX) || defined(OS_FUCHSIA)
#include "base/strings/string_util_posix.h"
#include "starboard/types.h"
#error Define string operations appropriately for your platform