Manage Textual Information by Using Strings

To use textual data to control chart behavior and to manipulate text to create natural language output, use strings. String data is available only in Stateflow^® charts that use C as the action language.

Example of String Data

In Stateflow, a string is a piece of text surrounded by quotes ("..." or '...'). For example, this chart takes string data as input. Based on that input, the chart produces a corresponding string output.

To specify a string symbol, set its Type field to string. Stateflow dynamically allocates memory space for this type of data.

Alternatively, you can create string data with a maximum number of characters. To specify a string symbol with a buffer size of n characters, set its Type field to stringtype(n). The text of the string can be shorter than the buffer, but if it exceeds the buffer size, then the text in the string is truncated. For instance, if the symbol output in the previous chart is specified as stringtype(10), then its value in the state On is truncated to "All system". Depending on the configuration parameter String truncation checking, you can halt simulation and diagnose truncation of string data.

String Truncation Checking	Description
`error`	Simulation stops with an error.
`warning`	String is truncated. Simulation continues with a warning.
`none`	String is truncated. Simulation continues with no error or warning.

Note

Unlike C or C++, Stateflow interprets escape sequences as literal characters. For example, the string "\n" contains two characters, backslash and n, and not a newline character.

Computation with Strings

To manipulate string data in a Stateflow chart, use the operators listed in this table.

Operator	Syntax	Description	Example
`strcpy`	`strcpy(dest,src)`	An alternative way to execute `dest = src`.	Assign string data to `s1`, `s2`, and `s3`. strcpy(s1,'So long'); strcpy(s2,"Farewell"); strcpy(s3,s2);
`strcpy`	`dest = src`	Assigns string `src` to `dest`.	Assign string data to `s4`, `s5`, and `s6`. s4 = 'Auf Wiedersehen'; s5 = "Adieu"; s6 = s4;
`strcat`	`dest = strcat(s1,...,sN)`	Concatenates strings `s1,...,sN`.	Concatenate strings to form `"Stateflow"`. s1 = "State"; s2 = "flow"; dest = strcat(s1,s2);
`substr`	`dest = substr(str,i,n)`	Returns the substring of length `n` starting at the `i`-th character of string `str`. Use zero-based indexing.	Extract substring `"Stateflow"` from a longer string. str = "Stateflow, rule the waves!"; dest = substr(str,0,9);
`tostring`	`dest = tostring(X)`	Converts numeric, Boolean, or enumerated data to string.	Convert numeric value to string `"1.2345"`. dest = tostring(1.2345);
			Convert Boolean value to string `"true"`. dest = tostring(1==1);
			Convert enumerated value to string `"RED"`. dest = tostring(RED);
`strcmp`	`tf = strcmp(s1,s2)`	Compares strings `s1` and `s2`. Returns `0` if the two strings are identical. Otherwise returns a nonzero integer. The sign of the output value depends on the lexicographic ordering of the input strings `s1` and `s2`. The magnitude of the output value depends on the compiler that you use. This value can differ in simulation and generated code. Strings are considered identical when they have the same size and content. This operator is consistent with the C library function `strcmp` or the C++ function `string.compare`, depending on the compiler that you select for code generation. The operator behaves differently than the function `strcmp` in MATLAB^®.	Return a value of `0` (strings are equal). tf = strcmp("abc","abc");
	`tf = strcmp(s1,s2)`		Return a nonzero value (strings are not equal). tf = strcmp("abc","abcd");
	`s1 == s2`	An alternative way to execute `strcmp(s1,s2) == 0`.	Return a value of `true`. "abc" == "abc";
	`s1 != s2`	An alternative way to execute `strcmp(s1,s2) != 0`.	Return a value of `true`. "abc" != "abcd";
	`tf = strcmp(s1,s2,n)`	Returns `0` if the first `n` characters in `s1` and `s2` are identical.	Return a value of `0` (substrings are equal). tf = strcmp("abc","abcd",3);
`strlen`	`L = strlen(str)`	Returns the number of characters in the string `str`.	Return a value of `9`. L = strlen("Stateflow");
`str2double`	`X = str2double(str)`	Converts the text in string `str` to a double-precision value. `str` contains text that represents a number. Text that represents a number can contain: Digits A decimal point A leading `+` or `-` sign An `e` preceding a power of 10 scale factor If `str2double` cannot convert text to a number, then it returns a `NaN` value.	Return a value of `-12.345`. X = str2double("-12.345");
`str2double`	`X = str2double(str)`		Return a value of `123400`. X = str2double("1.234e5");
`str2ascii`	`A = str2ascii(str,n)`	Returns array of type `uint8` containing ASCII values for the first `n` characters in `str`, where `n` is a positive integer. Use of variables or expressions for `n` is not supported.	Return `uint8` array `{72,101,108,108,111}`. A = str2ascii("Hello",5);
`ascii2str`	`dest = ascii2str(A)`	Converts ASCII values in array `A` of type `uint8` to string.	Return string `"Hi!"`. A[0] = 72; A[1] = 105; A[2] = 33; dest = ascii2str(A);

Where to Use Strings

Use string data at these levels of the Stateflow hierarchy:

Chart
Subchart
State

Use string data as arguments for:

State actions
Condition and transition actions
Graphical functions
Simulink^® functions
Truth table functions that use C as the action language

If you have Simulink Coder™ installed, you can use string data for simulation and code generation.

Documentation