--- title: "basic_string" --- {{< callout type="info">}} Header: `string.h` `wstring.h` `u8string.h` `u16string.h` `u32string.h` Similar to: `std::string` `std::wstring` `std::u8string` `std::u16string` `std::u32string` {{< /callout >}} Fixed capacity string classes. ```cpp etl::string etl::wstring etl::u8string etl::u16string etl::u32string ``` ```cpp etl::string_ext etl::wstring_ext etl::u16string_ext etl::u32string_ext ``` Inherits from `etl::istring`, `etl::iwstring`, `etl::iu8string`, `etl::iu16string` or `etl::iu32string`. The base classes may be used as a size independent pointer or reference type for any string instance. Has the ability to be copied by low level functions such as `memcpy` by use of a `repair()` function. See the function reference for an example of use. Note: `cstring.h` is deprecated ## Macros If `ETL_DISABLE_STRING_TRUNCATION_CHECKS` is defined then the string will not be checked for truncation and the truncation functions will not be available. If `ETL_DISABLE_STRING_CLEAR_AFTER_USE` is defined then the string will not be cleared after use and the 'secure' functions will not be available. Defining both of these macros can reduce the overhead of an `etl::string` by up to 4 bytes. If `ETL_ENABLE_ERROR_ON_STRING_TRUNCATION` is defined then an error will be asserted if the string would truncate. ## External buffers ```cpp etl::string_ext etl::wstring_ext etl::u16string_ext etl::u32string_ext ``` With these templates, a pointer to an external buffer, plus the size of the buffer must be supplied at construction. **Note** The buffer size must include room for a terminating null. **Example** ```cpp constexpr size_t Size = 10; // A string of a maximum of 10 characters, using an internal buffer. etl::string text; // A string of a maximum of 10 characters, using an external buffer. char buffer[Size + 1]; etl::string_ext text(buffer, etl::size(buffer)); ``` --- If the external buffer contains a C string and you wish this to be the initial value, then use the following constructor with the buffer as the initial text parameter. ```cpp etl::string_ext text(buffer, buffer, etl::size(buffer)); ``` This constructs a string of capacity `etl::size(buffer)` containing the null terminated string in buffer. The constructor will detect that the initial text and the buffer are at the same address. --- **Note** When using external buffered strings, a `memcpy` + `repair` will **not** produce a copy of the string. Both the original and copy will point to the same external buffer. ## Truncation Strings contain an internal flag that records the truncation state. If a string Is constructed, assigned or modified in any way such that the text contained would have exceeded the capacity then the truncate flag is set. The string will be truncated at the maximum capacity. A string may become marked as truncated if it is assigned characters or constructed from another string marked as truncated. This will occur even if the resulting string is not truncated itself. The truncation flag is cleared if the string is assigned from a string that does not exceed the capacity or a non-truncated string. It can also be forcibly cleared by calling `clear_truncated()`. If it is required that truncation be an error then define `ETL_STRING_TRUNCATION_IS_ERROR`. --- ```cpp bool truncated() const ``` **Description** Returns `true` if the string was truncated (the assigned or inserted string was greater than capacity or marked as truncated), otherwise `false`. --- ```cpp void clear_truncated() ``` **Description** Clears the internal truncated flag. --- **Example** Assuming `ETL_STRING_TRUNCATION_IS_ERROR` is not defined. ```cpp etl::string<11> text1 = "Hello"; // Not truncated. etl::string<6> text2 = " World!!!"; // Truncated to " World". text1 += text2; // Truncated. text1 inherits the truncation state from text2. text1.assign("Hello World"); // Not truncated. ``` ## Interfacing with C APIs The ETL strings implement three functions to ease interfacing with C APIs. ```cpp initialize_free_space() trim_to_terminator() data_end() ``` --- ```cpp initialize_free_space() ``` **Description** Initializes the free space in the string to null terminators. Since: `20.3.0` --- ```cpp trim_to_terminator() ``` **Description** Sets the string length to the first terminating null or the max size if the string. Since: `20.3.0` --- ```cpp data_end() ``` **Description** Returns a pointer to the current terminating null. Since: `20.3.0` **Example** ```cpp // Send the ETL string data to a C function that will append characters. etl::string<20> text("Hello "); text.initialize_free_space(); // If the C function does not add its own null terminators. CFunction(text.data_end(), text.available()); text.trim_to_terminator(); ``` --- ## Member types ```cpp value_type T size_type size_t difference_type ptrdiff_t reference value_type& const_reference const value_type& pointer value_type* const_pointer const value_type* iterator Random access iterator const_iterator Constant random access iterator reverse_iterator ETL_OR_STD::reverse_iterator const_reverse_iterator ETL_OR_STD::reverse_iterator ``` ## Constructor **Internal buffer** ```cpp etl::string(); etl::string(const istring& str); etl::string(const istring& str, size_t pos, size_t len = npos); etl::string(const char* s); etl::string(const char* s, size_t n); etl::string(size_t n, char c); etl::string(const etl::string_view& view); ``` --- ```cpp template etl::string(TIterator begin, TIterator end); ``` **Description** Truncates the string if too long. **External buffer** ```cpp etl::string(char* buffer, size_t buffer_size); etl::string(const istring& str, char* buffer, size_t buffer_size); etl::string(const istring& str, char* buffer, size_t buffer_size, size_t pos, size_t len = npos); etl::string(const char* s, char* buffer, size_t buffer_size); etl::string(const char* s, size_t n, char* buffer, size_t buffer_size); etl::string(size_t n, char c, char* buffer, size_t buffer_size); etl::string(const etl::string_view& view, char* buffer, size_t buffer_size); ``` ```cpp template etl::string(TIterator begin, TIterator end, char* buffer, size_t buffer_size); ``` Truncates the string if too long. ## Element access ```cpp T& at(size_t i) const T& at(size_t i) const ``` Returns a reference or const reference to the indexed element. Emits an etl::string_out_of_bounds if the index is out of range of the array. --- ```cpp T& operator[](size_t i) const T& operator[](size_t i) const ``` Returns a reference or const reference to the indexed element. --- ```cpp T& front() const T& front() const ``` Returns a reference or const reference to the first element. Undefined behaviour if the string is empty. --- ```cpp T& back() const T& back() const ``` Returns a reference or const reference to the last element. Undefined behaviour if the string is empty. ## Iterators ```cpp iterator begin() const_iterator begin() const const_iterator cbegin() const ``` Returns an iterator to the beginning of the string. --- ```cpp iterator end() const_iterator end() const const_iterator cend() const ``` Returns an iterator to the end of the string. --- ```cpp iterator rbegin() const_reverse_iterator rbegin() const const_reverse_iterator crbegin() const ``` Returns a reverse iterator to the beginning of the string. --- ```cpp iterator rend() const_reverse_iterator rend() const const_reverse_iterator crend() const ``` Returns a reverse iterator to the end of the string. --- ```cpp value_type* data() const value_type* data() const ``` Returns a pointer to the start of the string. --- ```cpp value_type* data_end() const value_type* data_end() const ``` Returns a pointer to the terminator of the string. ## Capacity ```cpp bool empty() const ``` Returns true if the size of the string is zero, otherwise false. --- ```cpp bool full() const ``` Returns true if the size of the string is SIZE, otherwise false. --- ```cpp size_t size() const ``` Returns the size of the vector. --- ```cpp void resize(size_t new_size, T value = T()) ``` Resizes the string, up to the maximum capacity. Emits an etl::string_full if the string does not have the capacity. --- ```cpp template void resize_and_overwrite(size_type new_size, TOperation operation) ``` Resizes the string and overwrites to data using the operation. Since: `20.39.5` --- ```cpp void uninitialized_resize(size_t new_size) ``` Resizes the string, up to the maximum capacity, without initialising the new elements. Since: `20.4.0` --- ```cpp size_t max_size() const ``` Returns the maximum possible size of the string. --- ```cpp size_t capacity() const ``` Returns the maximum possible size of the string. --- ```cpp size_t available() const ``` Returns the remaining available capacity in the string. --- ## Modifiers ```cpp void push_back(value_type value) ``` Pushes a value to the back of the string. No action if the string is already full. --- ```cpp void pop_back(); ``` Pop a value from the back of the string. No action if the string is already empty. ## Insert ```cpp iterator insert(iterator position, T value) ``` Upto: `20.19.0` --- ```cpp iterator insert(iterator position, size_type n, T value) ``` --- ```cpp template iterator insert(iterator position, TIterator first, TIterator last) ``` --- ```cpp iterator insert(const_iterator position, T value) ``` Since: `20.20.0` --- ```cpp iterator insert(const_iterator position, size_type n, T value) ``` --- ```cpp template iterator insert(const_iterator position, TIterator first, TIterator last) ``` --- ```cpp etl::istring& insert(size_type position, const etl::istring& str) ``` --- ```cpp etl::istring& insert(size_type position, const etl::string_view& view) Since: `20.39.5` --- ```cpp etl::istring& insert(size_type position, const etl::istring& str, size_type subposition, size_type sublength) ``` --- ```cpp etl::istring& insert(size_type position, const etl::string_view& view, size_type subposition, size_type sublength) ``` Since: `20.39.5` --- ```cpp etl::istring& insert(size_type position, const_pointer s) ``` --- ```cpp etl::istring& insert(size_type position, const_pointer s, size_type n) ``` --- ```cpp etl::istring& insert(size_type position, size_type n, value_type c) ``` Inserts values in to the string. Truncates the string if too long. Note: Strings that insert from themselves are only supported if the insert position is after the input range. ## Erase ```cpp etl::istring& erase(size_type position, size_type length_ = npos) ``` --- ```cpp iterator erase(iterator i_element) iterator erase(iterator first, iterator last) ``` Upto: `20.19.0` --- ```cpp iterator erase(iterator i_element) iterator erase(const_iterator i_element) iterator erase(const_iterator first, const_iterator last) ``` Erases values in the string. Iterators are not checked. Since: `20.20.0` ## Assign ```cpp template void assign(TIterator begin, TIterator end); ``` --- ```cpp void assign(size_t n, value_type value); ``` Fills the vector with the values. Emits `etl::string_iterator` if the distance between begin and end is illegal. Truncates the string if too long. ```cpp void assign(const etl::istring& str); void assign(const etl::string_view& str); 20.40.0 void assign(const std::string_view& str); void assign(const etl::istring& str, size_t subpos, size_t sublen); void assign(const char* s); void assign(const char* s, size_t n); void assign(size_t n, char c); ``` ```cpp template void assign(TIterator first, TIterator last); ``` Assigns to the string. Truncates the string if too long. May inherit the truncation state if the parameter is an `etl::string`. --- ## Append ```cpp etl::istring& append(const etl::istring& str); etl::istring& append(const etl::istring& str, size_t subpos, size_t sublen); etl::istring& append(const etl::string_view& view); etl::istring& append(const etl::string_view& view, size_t subpos, size_t sublen); etl::istring& append(const char* s); etl::istring& append(const char* s, size_t n); etl::istring& append(size_t n, char c); ``` ```cpp template string& append(TIterator first, Titerator last); ``` Appends to the string. Truncates the string if too long. May inherit the truncation state if the parameter is an `etl::string`. --- ## Insert ```cpp etl::istring& insert(size_t pos, const istring& str); etl::istring& insert(size_t pos, const istring& str, size_t subpos, size_t sublen); etl::istring& insert(size_t pos, const string_view& view); etl::istring& insert(size_t pos, const string_view& view, size_t subpos, size_t sublen); etl::istring& insert(size_t pos, const char* s); etl::istring& insert(size_t pos, const char* s, size_t n); etl::istring& insert(size_t pos, size_t n, char c); void insert (iterator p, size_t n, char c); iterator insert(iterator p, char c); ``` ```cpp template void insert (iterator p, Titerator first, Titerator last); ``` Inserts into the string. May inherit the truncation state if the parameter is an `etl::string`. Note: Strings that insert from themselves are only supported if the insert position is after the input range. --- ## Replace ```cpp string& replace(size_t pos, size_t len, const etl::istring& str); string& replace(iterator i1, iterator i2, const etl::istring& str); string& replace(size_t pos, size_t len, const etl::istring& str, size_t subpos, size_t sublen); string& replace(size_t pos, size_t len, const char* s); string& replace(iterator i1, iterator i2, const char* s); string& replace(size_t pos, size_t len, const char* s, size_t n); string& replace(iterator i1, iterator i2, const char* s, size_t n); string& replace(size_t pos, size_t len, size_t n, char c); string& replace(iterator i1, iterator i2, size_t n, char c); ``` ```cpp template string& replace(iterator i1, iterator i2, Titerator first, Titerator last); ``` Replaces parts of the string. Truncates the string if too long. May inherit the truncation state if the parameter is an `etl::istring`. --- ## Repair ```cpp void repair() ``` This function must be called if the string has been copied via a low level method such as `memcpy`. This can only be called from an `etl::string`, `etl::wstring`, `etl::u8string`, `etl::u16string`, or `etl::u32string` instance. If `ETL_ISTRING_REPAIR_ENABLE` is defined then `repair()` may be called from the `etl::istring` base class. Be aware that doing this introduces a virtual function to the class. Has no effect if the object has not been copied in this way. **Example** ```cpp typedef etl::string<10> String; String text = "ABCDEF"; char buffer[sizeof(String)]; memcpy(&buffer, &text, sizeof(String)); String& rtext(*reinterpret_cast(buffer)); // Do not access the string in any way until you have called this. rtext.repair(); ``` --- ```cpp void clear(); ``` Clears the string to a size of zero. Resets the truncate flag --- ```cpp void initialize_free_space() ``` This function will initialize the free space in a string to null terminators. --- ```cpp void trim_to_terminator() ``` The string length will be set to the position of the first null terminator. If the last item in the buffer is not a null terminator then one will be inserted. --- ```cpp string& operator = (const etl::istring& rhs) string& operator = (const value_type* text) ``` ## Assignment operator. May inherit the truncation state is the parameter is an `etl::string`. ```cpp string& operator += (const etl::istring& rhs) string& operator += (const value_type* text) ``` ## Addition operator. May inherit the truncation state is the parameter is an `etl::istring`. ```cpp void clear(); ``` Clears the string to a size of zero. Resets the truncate flag. ## Find ```cpp size_t find(const etl::istring& str, size_t pos = 0) const; size_t find(const char* s, size_t pos = 0) const; size_t find(const char* s, size_t pos, size_t n) const; size_t find(char c, size_t pos = 0) const; ``` ## Find in a string ```cpp size_t rfind(const etl::istring& str, size_t pos = npos) const; size_t rfind(const char* s, size_t pos = npos) const; size_t rfind(const char* s, size_t pos, size_t n) const; size_t rfind(char c, size_t pos = npos) const; ``` Reverse find in a string --- ```cpp size_t find_first_of(const string& str, size_t pos = 0) const; size_t find_first_of(const char* s, size_t pos = 0) const; size_t find_first_of(const char* s, size_t pos, size_t n) const; size_t find_first_of(char c, size_t pos = 0) const; ``` Find first of in a string --- ```cpp size_t find_last_of(const etl::istring& str, size_t pos = npos) const; size_t find_last_of(const char* s, size_t pos = npos) const; size_t find_last_of(const char* s, size_t pos, size_t n) const; size_t find_last_of(char c, size_t pos = npos) const; ``` Find last of in a string. --- ```cpp size_t find_first_not_of(const etl::istring& str, size_t pos = 0) const; size_t find_first_not_of(const char* s, size_t pos = 0) const; size_t find_first_not_of(const char* s, size_t pos, size_t n) const; size_t find_first_not_of(char c, size_t pos = 0) const; ``` Find first not of in a string --- ```cpp size_t find_last_not_of(const etl::istring& str, size_t pos = npos) const; size_t find_last_not_of(const char* s, size_t pos = npos) const; size_t find_last_not_of(const char* s, size_t pos, size_t n) const; size_t find_last_not_of(char c, size_t pos = npos) const; ``` Find last not of in a string --- ## contains ```cpp bool contains(const etl::ibasic_string& str) const ``` Checks that the string is within this string. --- ```cpp template bool contains(const etl::basic_string_view& view) const ``` Checks that the view is within this string --- ```cpp bool contains(const_pointer s) const ``` Checks that text is within this string --- ```cpp bool contains(value_type c) const ``` Checks that character is within this string ## starts_with ```cpp bool starts_with(const etl::ibasic_string& str) const ``` Checks that the string is the start of this string --- ```cpp template bool starts_with(const etl::basic_string_view& view) const ``` Checks that the view is the start of this string --- ```cpp bool starts_with(const_pointer s) const ``` Checks that the string is the start of this string -- ```cpp bool starts_with(value_type c) const ``` Checks that the character is the start of this string ## ends_with ```cpp bool ends_with(const etl::ibasic_string& str) const ``` Checks that the string is the end of this string --- ```cpp template bool ends_with(const etl::basic_string_view& view) const ``` Checks that the view is the end of this string --- ```cpp bool ends_with(const_pointer s) const ``` Checks that the string is the end of this string --- ```cpp bool ends_with(value_type c) const ``` Checks that the character is the end of this string --- ## Substr ```cpp string substr(size_t pos = 0, size_t len = npos) const ``` Extract a substring --- ## Compare ```cpp int compare(const etl::istring& str) const; int compare(size_t pos, size_t len, const etl::istring& str) const; int compare(size_t pos, size_t len, const etl::istring& str, size_t subpos, size_t sublen) const; int compare(const char* s) const; int compare(size_t pos, size_t len, const char* s) const; int compare(size_t pos, size_t len, const char* s, size_t n) const; ``` ## Compare strings --- ## Non-member functions Make a string from a literal or array `char` ```cpp template etl::string make_string(const char (&text) [Max_Size]) ``` --- ```cpp template etl::string make_string_with_capacity(const char (&text) [Size]) ``` --- `wchar_t` ```cpp template etl::wstring make_string(const wchar_t (&text) [Max_Size]) ``` ```cpp template etl::wstring make_string_with_capacity(const wchar(&text) [Size]) ``` --- `char8_t` Since: `20.38.7` ```cpp template etl::u8string make_string(const char8_t (&text) [Max_Size]) ``` --- ```cpp template etl::u16string make_string_with_capacity(const char16_t(&text) [Size]) ``` `char16_t` ```cpp template etl::u16string make_string(const char16_t (&text) [Max_Size]) ``` --- ```cpp template etl::u16string make_string_with_capacity(const char16_t(&text) [Size]) --- `char32_t` ```cpp template etl::u32string make_string(const char32_t (&text) [Max_Size]) ``` --- ```cpp template etl::u32string make_string_with_capacity(const char32_t(&text) [Size]) ``` ## Examples ```cpp // 'text' contains "Hello World" with a size and capacity of 11. auto text = etl::make_string("Hello World"); // 'text' contains "Hello World" with a size of 11 and capacity of 20. auto text = etl::make_string_with_capacity<20>("Hello World"); // 'text' contains "Hello Worl" with a size of 10 and capacity of 10. Marked as truncated. auto text = etl::make_string_with_capacity<10>("Hello World"); ``` ## Comparisons `==` `true` if the contents of the vectors are equal, otherwise `false`. `!=` `true` if the contents of the vectors are not equal, otherwise `false`. `< ` `true` if the contents of the lhs are lexicographically less than the contents of the rhs, otherwise `false`. `<=` `true` if the contents of the lhs are lexicographically less than or equal to the contents of the rhs, otherwise `false`. `> ` `true` if the contents of the lhs are lexicographically greater than the contents of the rhs, otherwise `false`. `>=` `true` if the contents of the lhs are lexicographically greater than or equal to the contents of the rhs, otherwise `false`.