Question

I am using VC++ 2008 express edition for C. When I try to run this:

/* Demonstrates printer output. */

#include <stdio.h>

main()
{ 
 float f = 2.0134;

 fprintf(stdprn, "This message is printed.\n\n");
 fprintf(stdprn, "And now some numbers:\n\n");
 fprintf(stdprn, "The square of %f is %f.", f, f*f);

 /* Send a form feed */

 fprintf(stdprn, "\f");
}

I get four of these errors: error C2065: ‘stdprn’ : undeclared identifier.

On this forum, they wrote that it works to define the printer as follows:

FILE *printer;
printer = fopen("PRN", "w");

EDIT
It builds with a warning that fopen is unsafe. When it runs the error appears:

Debug Assertion fails.
File: f:\dd\vctools\crt_bld\self_x86\crt\src\fprintf.c
Line: 55

Expression: (str != NULL)

Answer 1

The stdprn stream was an extension provided by Borland compilers – as far as I know, MS have never supported it. Regarding the use of fopen to open the printer device, I don’t think this will work with any recent versions of Windows, but a couple of things to try:

• use PRN: as the name instead of PRN (note the colon)
• try opening the specific device using (for example) LPT1: (once again, note the colon). This will of course not work if you don’t have a printer attached.
• don’t depend on a printer dialog coming up – you are not really using the WIndows printing system when you take this approach (and so it probably won’t solve your problem, but is worth a try).