Basic PDS 7.00 "Program Memory Overflow" with Too Many CONST (61349)

SUMMARY

When used with the /V switch, the BC.EXE compiler that comes with Microsoft Basic Professional Development System (PDS) version 7.00 produces a "Program memory overflow" error when compiling a program that has approximately 680+ CONSTants. The compiler can still have up to 13K "bytes free" of compiler workspace when reporting this error.

"Program memory overflow" also occurs when compiling the TEST1.BAS program generated below using 756+ CONSTants with the BC /Fs (far strings) option.

The CONST limits are improved in Basic PDS version 7.10, which can handle significantly more CONSTants than Basic 7.00.

The error message "Program memory overflow" is misleading because normally the compiler only gives that error when more than 64K of code has been generated for the module being compiled. This error represents a limitation of the compiler. This error is generated when the number of CONSTants that can be included in a Basic module has been exceeded.

MORE INFORMATION

The "Program memory overflow" error above is due to the amount of internal overhead that the compiler sets aside to do its work with CONSTants. The error message is not generated because of a lack of compiler workspace. In this case, 13K "bytes free" is a valid number. There is actually 13K of compiler workspace free. A different limitation has been encountered -- the number of CONSTants BC.EXE can handle.

The BC.EXE in QuickBasic version 4.50 and the BC.EXE compiler in Basic versions 6.00b and 7.10 will successfully compile a program with over 1000 CONSTants.

Illustration

To demonstrate the limitation in 7.00, use the FIRST.BAS program below to create the Basic program TEST1.BAS with "n" number of CONSTants. For example, a TEST1.BAS program created with approximately 650 CONSTants will compile with no errors in Basic PDS 7.00. A program with 680+ CONSTants compiled with BC /V gives "Program-memory overflow" in Basic PDS 7.00.

As a comparison to versions earlier than 7.00, if you create a TEST1.BAS program with 1000 CONSTants, it will compile correctly with BC.EXE 4.50 and BC.EXE 6.00b (which have a greater capacity for CONSTants than 7.00).

As a comparison to 7.10, in TEST1.BAS created below, 7.10 can handle 1100 CONSTants when compiled BC /V (but 1200 CONSTants gives "Program memory overflow"). In TEST1.BAS created below, 7.10 can handle 2100 CONSTants when compiled BC /Fs (but 2200 CONSTants gives "Compiler out of memory, 0 bytes free"). Basic 7.10 can thus handle many more CONSTants than 7.00.

FIRST.BAS

FIRST.BAS prompts you for a number, and then creates another Basic program, TEST1.BAS, with that many CONSTants. Compile the resulting TEST1.BAS with BC /V or /Fs to test for compiler limitations.

   DEFINT A-Z
   CLS
   INPUT "How many CONSTants to you want in the file: ", Num%
   OPEN "test1.bas" FOR OUTPUT AS #1
   beg$ = "CONST p"
   equals$ = " ="
   FOR i = 1 TO Num%
      constant$ = beg$ + LTRIM$(RTRIM$(STR$(i))) + equals$ + STR$(i)
      PRINT #1, constant$
   NEXT
   CLOSE
   PRINT "File 'test.bas' successfully created"
   END