Description: Documentation

## function error

### Synopsis

Generate an error condition

### Usage

error (String_Type msg

### Description

The error function generates a SLang error condition causing the interpreter to start unwinding to top-level. It takes a single string parameter which is displayed on the stderr output device. The error condition may be cleared via an ERROR_BLOCK with the _clear_error function. Consult \user-manual for more information.

### Example

        define add_txt_extension (file)
        {
           if (typeof (file) != String_Type)
             error ("add_extension: parameter must be a string");
           file += ".txt";
           return file;
        }

### See also

verror , _clear_error , message

## function message

### Synopsis

Print a string onto the message device

### Usage

message (String_Type s

### Description

The message function will print the string specified by s onto the message device.

### Example

         define print_current_time ()
         {
           message (time ());
         }

### Notes

The message device will depend upon the application. For example, the output message device for the jed editor correspond to the line at the bottom of the display window. The default message device is the standard output device.

### See also

vmessage , sprintf , error

## function usage

### Synopsis

Generate a usage error

### Usage

usage (String_Type msg)

### Description

The usage function generates a usage exception and displays msg to the message device.

### Example

Suppose that some function plot plots an array of x and y values. The such a function could be written to issue a usage message if the wrong number of arguments were passed:

        define plot ()
        {
           variable x, y;

           if (_NARGS != 2)
             usage ("plot (x, y)");

           (x, y) = ();
           % Now do the hard part
              .
    	  .
        }

### See also

error , message

## function verror

### Synopsis

Generate an error condition

### Usage

verror (String_Type fmt, ...)

### Description

The verror function performs the same role as the error function. The only difference is that instead of a single string argument, verror takes a sprintf style argument list.

### Example

        define open_file (file)
        {
           variable fp;

           fp = fopen (file, "r");
           if (fp == NULL) verror ("Unable to open %s", file);
           return fp;
        }

### Notes

In the current implementation, strictly speaking, the verror function is not an intrinsic function. Rather it is a predefined SLang function using a combination of Sprintf and error .

### See also

error , Sprintf , vmessage

## function vmessage

### Synopsis

Print a formatted string onto the message device

### Usage

vmessage (String_Type fmt, ...)

### Description

The vmessage function formats a sprintf style argument list and displays the resulting string onto the message device.

### Notes

In the current implementation, strictly speaking, the vmessage function is not an intrinsic function. Rather it is a predefined SLang function using a combination of Sprintf and message .

### See also

message , Sprintf , verror