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string

Description

Strings are represented as arrays of type char and are null-terminated.

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

  • 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

Null termination

Generally, strings are terminated with a null character (ASCII code 0). This allows function (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.

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 by 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.

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').

Wrapping long strings

You can wrap long strings like this:

char myString[] = "This is the first line"
" this is the second line"
" etcetera";

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