Q28166: QB Uses Up Default String Space When Concatenating Far String
Article: Q28166 Product(s): See article Version(s): 6.00 6.00b 7.00 | 6.00 6.00b 7.00 Operating System(s): MS-DOS | OS/2 Keyword(s): ENDUSER | B_QuickBas | mspl13_basic Last Modified: 2-FEB-1990 Problem: When running the program below inside the QB.EXE environment, after about 72 iterations of concatenating a variable-length string onto a fixed-length string, an "Out of String Space" error is generated. However, the FRE("") and FRE(-1) functions both return the same value all the way through the loop. Note that the array of fixed-length strings is dynamically allocated, putting it into the far heap. The program runs properly when compiled and run as an EXE file. Response: The problem is that QuickBASIC assumes that a far fixed-length string will always stay far. However, the BASIC run-time routines must have the string in DGROUP in order to manipulate it with string functions like LTRIM$ and RTRIM$. LTRIM$ and RTRIM$ require two copies of the string at one point, and the program eventually runs out of string space in the default data segment in DGROUP. This will also happen in a version of the program compiled with BC /O if the strings are made longer. This limitation of BASIC is inherent in its construction, and Microsoft currently has no plans to change this construction. The following is a code example: REM $DYNAMIC DIM srv(0) AS STRING * 28000 abc$ = STRING$(330,"0") srv(0) = abc$ FOR t = 1 to 79 srv(0) = RTRIM$(srv(0)) + abc$ PRINT t, LEN(RTRIM$(srv(0))), FRE(""), FRE(-1) NEXT t
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