Share String Data with Custom C Code

This example shows how to share string data between a Stateflow® chart and custom C code. You can export string data from a Stateflow chart to a C function by using the str2ascii operator. You can import the output of your C code as string data in a Stateflow chart by using the ascii2str operator. By sharing data with custom code, you can augment the capabilities of Stateflow and leverage the software to take advantage of your preexisting code. For more information, see Reuse Custom Code in Stateflow Charts.

This model contains a Stateflow chart that calls two functions from custom C code. During simulation, the chart takes as its input a string that contains text representing a floating-point number in exponential form. The chart consists of three states that:

• Search the input string for leading zeroes, a decimal point, and an e.

• Parse the string into double-precision numbers representing the significand and exponent parts of the input.

• Merge the numeric information into an output string expressing the input in scientific notation.

For example, if the input string is "0123.456e789", then the chart outputs the string "0123.456e789 means 1.23456 times ten to the 791th power".

Export String Data from Stateflow to C

You can use the str2ascii operator to convert string data into an array that you can export from a Stateflow chart to a custom C code function.

1. In the custom code function, declare the input variable as having type char*.

2. In the Stateflow chart, convert the string to an array of type uint8 by calling the operator str2ascii.

3. Call the custom code function by passing the uint8 array as an input.

For example, in the previous chart, the Search state converts the input string str to the uint8 array Asrt. The Search state passes this array as an input to the custom code function searchfun:

extern void searchfun(int* nout, char* strin)
{
   nout[0] = strspn(strin,"0");
   nout[1] = strcspn(strin,".e");
   nout[2] = strcspn(strin,"e");
   nout[3] = strlen(strin);
}

The Search state calls this function with the command searchfun(n,Astr). The function populates the integer array n with these values:

• n[0] contains the number of leading zeroes in the input string str.

• n[1] contains the number of characters before the first instance of a decimal point or e. This result provides the number of characters before the decimal point in str.

• n[2] contains the number of characters before the first instance of e. This result provides the number of characters in the significand in str.

• n[3] contains the length of the input string str.

The Parse state uses these results to extract the values of the significand and exponent parts of the input.

Import String Data from C to Stateflow

You can import string data to a Stateflow chart by passing a pointer to an array of type uint8 as an input to a custom C function.

1. In the custom code function, declare the input variable containing the pointer as having type char*.

2. Save the output string data from the custom code function at the location indicated by the pointer.

3. In the Stateflow chart, convert the uint8 array to a string by calling the operator ascii2str.

For example, in the previous chart, the Merge state consolidates the numeric information obtained by the Parse state into an output string by calling the custom code function mergefun:

extern void mergefun(char* strout, char* strin, int in0, double in1, double in2)
{
   sprintf(strout, "%s means %1.*f times ten to the %dth power", strin, in0, in1, (int) in2);
}

The Merge state calls the mergefun function with the command mergefun(Asout,Astr,y0,y1,y2):

• Asout is an array of type uint8 pointing to the output of the custom function.

• Astr is an array of type uint8 corresponding to the input string to the chart.

• y0 is an integer containing the number of digits to the right of the decimal point in the significand.

• y1 and y2 are double-precision numbers representing the significand and exponent parts of the input.

The function mergefun calls the C library function sprintf, merging the contents of Astr, y1, and y2 and storing the result in the memory location indicated by Aout. The chart uses the operator ascii2str to convert this output to the string sout. In this way, the model imports the string constructed by the custom code function back into Stateflow.