Q(uick)BASIC Routine: StringLength

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StringLength

This routine is used in mixed-language programming. A non-BASIC routine uses StringLength to find the number of characters in a BASIC variable-length string

Worth knowing

Useful and cross-version information about the programming environments of QBasic and QuickBasic.

Syntax

length = StringLength(string-descriptor%);

Description/Parameter(s)

string-descriptor%

The near address of a string descriptor within a non-BASIC routine.

The preceding syntax is for the C language.
For C, MASM, Pascal, and FORTRAN examples, see Chapter 13, "Mixed-Language Programming with Far Strings" in the Programmer's Guide.

Usage Notes

Calls to the StringLength routine are usually made from a non-BASIC routine.
Note: If you are not doing mixed-language programming, there is usually no reason to use StringLength. Instead, use LEN to find the length of a variable-length string.
As an example, assume that a MASM routine takes a pointer to a string descriptor as a parameter. MASM can find the length of the string data by using the following code:
- ```
.model
```
```
extrn stringlength: far
```
```
.code
```
```
mov          ax, psdparm           ; offset of descriptor
```
```
push AX
```
```
call stringlength
```
The length of the string is returned in AX.
For detailed instructions on mixed-language programming with strings, see Chapter 12, "Mixed-Language Programming" and Chapter 13, "Programming with Near Strings" in the Programmer's Guide.

Example

This example uses the StringAssign routine to pass a BASIC string to an assembly-language program. The StringLength routine is used to determine the length of the string.
Note: To use this program, you must compile the following code and link it with the assembled MASM program (shown below in remarks) and the appropriate runtime library (BCL71ENR.LIB).

DEFINT A-Z
'Create a variable-length string.
Message1$ = "This string was sent to MASM for printing."
'Pass it to MASM to be printed.
CALL PrintMessage1(Message1$)
 
 
'; *************************PrintMessage1************************
';   This MASM procedure prints a string passed to it by BASIC.
'
'            .model      medium, basic       ;Use same model as BASIC
';Define external (BASIC library) procedures
'            extrn   StringAddress: far
'            extrn   StringLength: far
'
'            .code
';Define procedure with one word argument
'PrintMessage1  proc     uses ds,  descriptor
'
'            mov     ax, descriptor          ;Find length of string.
'            push        ax
'            call        StringLength
'            push        ax                  ;Save length on stack.
'
'            mov         ax, descriptor      ;Go find out the
'            push    ax                      ;address of the string
'            CALL    StringAddress           ;data.
'
'            mov         ds, dx              ;Address of string.l.
'            mov         dx, ax
'            mov     bx, 01                  ;Handle of printer.
'            pop     cx                      ;Length of string.
'            mov     ah, 40h                 ;Have DOS print it.
'            int         21h
'            ret
'PrintMessage1   endp
'
'            end