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diff --git a/docs/source/arduino/string.rst b/docs/source/arduino/string.rst index b841728..8db400a 100644 --- a/docs/source/arduino/string.rst +++ b/docs/source/arduino/string.rst @@ -1,158 +1,128 @@ +.. highlight:: cpp + .. _arduino-string: -string -====== +Strings +======= Description ----------- -Text strings can be represented in two ways. you can use the String -data type, which is part of the core as of version 0019, or you can -make a string out of an array of type char and null-terminate it. -This page described the latter method. For more details on the -String object, which gives you more functionality at the cost of -more memory, see the -`String object <http://arduino.cc/en/Reference/StringObject>`_ -page. +Text strings can be represented in two ways. You can + +1. Use the :ref:`String <arduino-stringclass>` data type, which is +part of the core as of version 0.0.9, or +2. You can make a string out of an array of type :ref:`char +<arduino-char>` and null-terminate it. +This page describes the second method. Examples -------- -All of the following are valid declarations for strings. - -:: - - char Str1[15]; - char Str2[8] = {'a', 'r', 'd', 'u', 'i', 'n', 'o'}; - char Str3[8] = {'a', 'r', 'd', 'u', 'i', 'n', 'o', '\0'}; - char Str4[ ] = "arduino"; - char Str5[8] = "arduino"; - char Str6[15] = "arduino"; - - - -**Possibilities for declaring strings** - - +All of the following are valid declarations for strings:: + char str1[15]; + char str2[6] = {'m', 'a', 'p', 'l', 'e'}; + char str3[6] = {'m', 'a', 'p', 'l', 'e', '\0'}; + char str4[ ] = "maple"; + char str5[6] = "maple"; + char str6[15] = "maple"; -- Declare an array of chars without initializing it as in Str1 -- Declare an array of chars (with one extra char) and the compiler - will add the required null character, as in Str2 -- Explicitly add the null character, Str3 -- Initialize with a string constant in quotation marks; the - compiler will size the array to fit the string constant and a - terminating null character, Str4 -- Initialize the array with an explicit size and string constant, - Str5 -- Initialize the array, leaving extra space for a larger string, - Str6 +As you can see, there are several methods available for declaring and +initializing strings: +- Declare an array of ``char`` without initializing it, as with ``str1``. +- Declare an array of ``char`` (with one extra ``char``) and the + compiler will add the required null character, as with ``str2``. -**Null termination** +- Explicitly add the null character (``'\0'``), as with ``str3``. +- Initialize with a string constant in quotation marks (``"..."``); + the compiler will size the array to fit the string constant and a + terminating null character (``str4``). +- Initialize the array with an explicit size and string constant, + (``str5``). -Generally, strings are terminated with a null character (ASCII code -0). This allows functions (like Serial.print()) to tell where the -end of a string is. Otherwise, they would continue reading -subsequent bytes of memory that aren't actually part of the -string. +- Initialize the array, leaving extra space for a larger string + (``str6``). +Null Termination +---------------- +Generally, strings are terminated with a null character (`ASCII +<http://en.wikipedia.org/wiki/ASCII>`_ code 0). This allows functions +(like ``SerialUSB.print()``) to tell where the end of a string is. +Otherwise, they would continue reading subsequent bytes of memory that +aren't actually part of the string. -This means that your string needs to have space for one more -character than the text you want it to contain. That is why Str2 -and Str5 need to be eight characters, even though "arduino" is only -seven - the last position is automatically filled with a null -character. Str4 will be automatically sized to eight characters, -one for the extra null. In Str3, we've explicitly included the null -character (written '\\0') ourselves. - - +This means that your string needs to have space for one more character +than the text you want it to contain. That is why ``str2`` and +``str5`` need to be six characters, even though "maple" is only five +-- the last position is automatically filled with a NULL +character. ``str4`` will be automatically sized to six characters, one +for the extra null. In the case of ``str3``, we've explicitly included +the null character (written ``'\0'``) ourselves. Note that it's possible to have a string without a final null -character (e.g. if you had specified the length of Str2 as seven -instead of eight). This will break most functions that use strings, -so you shouldn't do it intentionally. If you notice something -behaving strangely (operating on characters not in the string), -however, this could be the problem. - - - -**Single quotes or double quotes?** - - - -Strings are always defined inside double quotes ("Abc") and -characters are always defined inside single quotes('A'). +character (e.g. if you had specified the length of ``str2`` as five +instead of six). This will break most functions that use strings, so +you shouldn't do it intentionally. If you notice something behaving +strangely (operating on characters not in the string), however, this +could be the problem. +Single quotes or double quotes? +------------------------------- +Strings are always defined inside double quotes (``"Abc"``) and +characters are always defined inside single quotes (``'A'``). -**Wrapping long strings** +Wrapping long strings +--------------------- - - -You can wrap long strings like this: - -:: +You can wrap long strings like this:: char myString[] = "This is the first line" - " this is the second line" - " etcetera"; - - - -**Arrays of strings** - + " this is the second line" + " etcetera"; +Arrays of Strings +----------------- It is often convenient, when working with large amounts of text, such as a project with an LCD display, to setup an array of strings. Because strings themselves are arrays, this is in actually an example of a two-dimensional array. - - -In the code below, the asterisk after the datatype char "char\*" +In the code below, the asterisk after the datatype char ``char *`` indicates that this is an array of "pointers". All array names are actually pointers, so this is required to make an array of arrays. Pointers are one of the more esoteric parts of C for beginners to -understand, but it isn't necessary to understand pointers in detail -to use them effectively here. - - - -Example -------- +understand, but it isn't necessary to understand pointers in detail to +use them effectively here:: -:: + char* myStrings[] = {"This is string 1", "This is string 2", + "This is string 3", "This is string 4", + "This is string 5", "This is string 6"}; - - char* myStrings[]={"This is string 1", "This is string 2", "This is string 3", - "This is string 4", "This is string 5","This is string 6"}; - - void setup(){ - Serial.begin(9600); - } - - void loop(){ - for (int i = 0; i < 6; i++){ - Serial.println(myStrings[i]); - delay(500); - } + void setup() { + SerialUSB.begin(); } + void loop() { + for (int i = 0; i < 6; i++) { + SerialUSB.println(myStrings[i]); + delay(500); + } + } See Also -------- - -- `array <http://arduino.cc/en/Reference/Array>`_ -- `PROGMEM <http://arduino.cc/en/Reference/PROGMEM>`_ -- `Variable Declaration <http://arduino.cc/en/Reference/VariableDeclaration>`_ - +- :ref:`array <arduino-array>` +- :ref:`__attribute__ <arm-gcc-attribute-flash>` +- :ref:`Variables <arduino-variables>` |