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authorPerry Hung <iperry@gmail.com>2011-01-24 23:23:29 -0500
committerPerry Hung <iperry@gmail.com>2011-01-24 23:23:29 -0500
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+.. highlight:: cpp
+
+.. _lang-string:
+
+Strings
+=======
+
+Text strings can be represented in two ways. You can
+
+1. Use the :ref:`String <lang-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
+<lang-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[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";
+
+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``.
+
+- 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``).
+
+- 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 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 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
+---------------------
+
+You can wrap long strings like this::
+
+ char myString[] = "This is the first line"
+ " 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 *``
+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::
+
+ 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() {
+ SerialUSB.begin();
+ }
+
+ void loop() {
+ for (int i = 0; i < 6; i++) {
+ SerialUSB.println(myStrings[i]);
+ delay(500);
+ }
+ }
+
+
+See Also
+--------
+
+- :ref:`array <lang-array>`
+- :ref:`__attribute__ <arm-gcc-attribute-flash>`
+- :ref:`Variables <lang-variables>`
+
+
+.. include:: cc-attribution.txt