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Thread: Data type of pointer

  1. #1

    Data type of pointer

    If I want to do a PEEK of a memory address that I got from VARPTR, then I need to know the data type of a pointer, right? So what is the data type of a pointer? I mean, obviously it's a numeric data type, and it's a memory address, so it can't be BYTE.

  2. #2

    Well, I didn't NEED to know

    I double checked the manual on PEEK, and saw that specifying the type was optional. This is the little experiment I was fooling with. I tried calling VARPT with PEEK and that gave me the value at the variable.

    USES "CONSOLE"                                  
    REM First, we declare variables a, b, and c     
    DIM a AS BYTE                                   
    DIM b AS BYTE                                   
    DIM c AS BYTE                                   
    REM Second, we assign a value to each variable  
    a = 1                                           
    b = 2                                           
    c = 3                                           
    REM Third, we print the address of each variable
    PRINTL VARPTR(a)                          
    PRINTL VARPTR(b)                                
    PRINTL VARPTR(c)
    
    So, I tried doing "PRINTL PEEK(VARPTR(a))" and that gave me the value at the variable, so I know that if I have the value stored at the pointer, I can use PEEK to get the value stored in the variable. I'm sure this is patently obvious to anyone that knows what they're doing.
    Last edited by Benjamin; 20-12-2023 at 04:18.

  3. #3
    thinBasic author ErosOlmi's Avatar
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    A pointer is a number that points to a memory area.

    thinBasic is a 32bit only process so under 32bit process, a pointer is 32bit so usually a DWORD but also a LONG is OK (internally the sign bit will not be interpreted as sign but will be part of the addressing)

    Under a 64bit process, memory addressing pointer is represented by a QUAD (64 bit number)

    What is allocated into a memory area and how it is interpreted is responsibility of the process and programmer.
    The Operating system is just responsible of allocating/deallocating but how that memory are is interpreted is not a OS job.
    The same memory area con be interpreted ad a number or a string or a type or whatever.

    Just an example
    USES "CONSOLE"                                 
    REM First, we declare variables a, b, and c     
    DIM a AS BYTE                                  
    DIM b AS BYTE                                  
    DIM c AS BYTE                                  
    REM Second, we assign a value to each variable  
    a = 1                                           
    b = 2                                           
    c = 3                                           
    REM Third, we print the address of each variable
    printl "Defined 3 byte var: a, b, c, d"
    printl "Values of a, b, c...........:", a,b,c
    PRINTL "Varptr of a, b, c...........:", VARPTR(a), VARPTR(b), VARPTR(c)
    PRINTL "Peek(Varptr) of a, b, c.....:", peek(byte, VARPTR(a)), peek(byte, VARPTR(b)), peek(byte, VARPTR(c))
    printl "-----------------------------"
    
    
    dim nLong as Long
    nlong = 1234567898
    printl "Defined 1 long var: nLong"
    printl "Values nLong...............:", nLong
    PRINTL "Varptr of nLong............:", VARPTR(nLong)
    PRINTL "Peek(Varptr) of nLong......:", peek(long, VARPTR(nLong))
    printl "-----------------------------"
    
    
    dim bArray(4) as byte at varptr(nLong)
    printl "Defined 1 array of 4 bytes at the memory location of nLong so the memory holding nLong can be interpreted in a different way"
    printl "Values bArray(1)...............:", bArray(1)
    printl "Values bArray(2)...............:", bArray(2)
    printl "Values bArray(3)...............:", bArray(3)
    printl "Values bArray(4)...............:", bArray(4)
    PRINTL "Varptr bArray..................:", VARPTR(bArray(1)), "Should be the same as VARPTR(nLong) above"
    
    
    WaitKey
    
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