Transcript ISS PowerPoint Presentation

Using EXTERN
Dave Doulton
Information Systems
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Contents
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What are EXTERN functions?
 How do you use them?
 How do you create them?
 Examples of usage.
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What are EXTERN Functions?
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EXTERN and EXTERNS are two functions held in
the extern.dll (Dynamically Linked Library).
 These functions can do anything you wish provided
you can create the dll.
 Your dll is placed in the SIR directory in place of the
supplied version.
 Note they can both take string or numeric
parameters which can do different things but only
return a numeric from EXTERN and a string from
EXTERNS
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How do you use them?
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EXTERN
num = EXTERN ( X )
Invokes a user-supplied external function from the EXTERN dll.
The function can take a numeric or string parameter and calls a
different user function for each case.
The extern.dll library supplied by SIR contains dummy functions
which return zero.
EXTERNS
str = EXTERNS ( X )
Invokes a user-supplied external function from the EXTERN dll.
The function can take a numeric or string parameter and calls a
different user function for each case.
The extern.dll library supplied by SIR contains dummy functions
which return blank (a zero length string).
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How do you create them?
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To create the functions you can used the supplied
template which can be found in the api/examples
subdirectory of the directory where SIR is installed.
Information Systems
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How do you create them?
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//
// Skeleton of user defined EXTERN function.
//
// Use this to build your own extern.dll to use the PQL EXTERN and EXTERNS functions.
// See the examples in the API directory.
//
#ifndef __StdCall
#ifdef _WIN32
#define __StdCall __stdcall
#else
#define __StdCall
#endif
#endif
//
// The sirdbms executable links to these functions as defined:
//
const char * __StdCall SIRExtern1 (char * buffer);
double __StdCall SIRExtern2 (char * buffer);
const char * __StdCall SIRExtern3 (double num);
double __StdCall SIRExtern4 (double num);
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How do you create them?
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//
// PQL Function str=EXTERNS(string)
//
const char * __StdCall SIRExtern1 (char * buffer) {
return "";
}
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//
// PQL Function num=EXTERN(string)
//
double __StdCall SIRExtern2 (char * buffer) {
return 0;
}
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//
// PQL Function str=EXTERNS(num)
//
const char * __StdCall SIRExtern3 (double num) {
return "";
}
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//
// PQL Function num=EXTERN(num)
//
double __StdCall SIRExtern4 (double num) {
return 0;
}
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Examples of usage
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David Baxter has made a dll that reads web pages.
 Note not all web pages can be read. It is a matter of
trial and error to check if the pages you want are
readable.
 The web addresses are entered without the http:// in
the version I am using and that will be available on
the SUG website.
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Examples of usage
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I have 5 example programs
1. Writing the contents of a web page to a file.
2. Reading Share prices from the msn money website.
3. Reading Weather information from the BBC weather
website.
4. Reading Train Live Running from the National rail
website.
5. Reading Formula 1 results from F1 web pages
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Examples of usage
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The descriptions of the extern functionality in this dll
are as follows:
 num=EXTERN(string)
 It takes a url filename and returns a socket id. It’s
quick and dirty and just goes to port 80
 str=EXTERNS(num)
 Num is the socket id from before and it returns a
single character at a time from the http server.
 num=EXTERN(num)
 Num is the socket id from before and cleans up.
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Examples of usage
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The example programs use a subprocedure to read
from the web server up to the next >.
 This usually results in fairly small chunks of text to
analyse.
 The lines are searched for predetermined text that
allows the extraction of the required data.
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Examples of usage
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See the example programs.
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Any Questions?
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