How can I pass a string as user-defined function parameter in CAPL

Question

In CAPL, apparently you cannot pass a string as an input parameter for a user-defined function, according to the docs (see CAPL Introduction » Data Types for Function Parameters).

I'm working with file handling, both in read and write directions. I'd like to refactor my code to use a function that accepts the filename as input parameter.

Apart from the obvious workarounds, such as using a global variable, using a system/environment variable, I'm interested in the possibility of other alternatives.

How do you do it?

edit

CAPL does not provide the string type, much like C these are "just" arrays of characters.

In the help page I was mentioning, you can pass a single char as parameter function, but not a char[] array.

What, rightfully, mr. Spiller points out is that this piece of code works:

on start
{
    function("a string");
}

void function(char string[])
{
    write ("my string is %s", string);
}

and outputs:

CAPL / .NET my string is a string

However, that looks like an associative array to me.

For instance, this compiles as well:

void function(int number[], char string[])
{
    // do stuff
}

But understanding what is going on is suddenly more difficult, as this won't compile:

on start
{
    function(13, "a string");
}

void function(int number[], char string[])
{
    write ("my number is %d", number);
    write ("my string is %s", string);
}

Error: types of parameters do not match.

Finally:

variables
{
    int associativeArray[ float ];
}

on start
{
    associativeArray[1] = 3;
    function(associativeArray, "a string");
}

void function(int number[float], char string[])
{
    for (float aKey: number)
    {
        write ("my number is %d(%f)", number[aKey], aKey);
    }
}

CAPL / .NET my number is 3(1.000000)

works as intended, but then again, I'm unsure of what the caveats of using an associative array are in this scenario (I can't find out a way of iterate over the string with the same syntax, for instance), and how do you address them, if you do.

Just to make sure we are on the same page: why do you think that you cannot pass a string? Why would `void func(char param[])` not work? — MSpiller, Feb 10 '20 at 09:20
Mostly due to the reference page I was mentioning. I'm not entirely sure about how you are making this work, to be honest. I'm editing my question to make it clearer. — Daemon Painter, Feb 10 '20 at 13:24

MSpiller · Accepted Answer · 2020-02-10T15:44:57.220

The help page you are mentioning also says further below something like

and matrices of the aforementioned datatypes (I can't remember the exact wording and don't have access to a CANoe right now).

char[], int[] and so on are not associative arrays but arrays. You may think of them as associative array but the key may only be a positive integer.

As you say CAPL and C handle strings in the same way, i.e. as arrays of characters. Therefore, coming back to your original question using a definition like

void func(char param[])

is the way to go when you want to pass a string (which is just an array of characters) to a function.

This:

on start
{
    function(13, "a string");
}

void function(int number[], char string[])
{
    write ("my number is %d", number);
    write ("my string is %s", string);
}

does not compile, because 13 is not an array of integers, but just a single integer. The compiler therefore says the the types do not match.

This will work:

on start
{
  int i[1];
  i[0] = 13;
  function(i, "a string");
}

The same way the following code will also NOT compile:

void function(char string[])
{
   ...
}

on start
{
  function('a');
}

'a' (note the single quotes) is just a single character and no array of characters and therefore the signature does not match.

You can get the individual characters of a string by simply using the [] operator (also same as in C).

char s[] = "abcde"; char c = s[2];

will store 'c' into s

Hope that explains it. Feel free to ask for further clarification. (I did type all this from top of my head, so please excuse any minor syntax errors)

How can I pass a string as user-defined function parameter in CAPL

1 Answers1