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allocating_20arrays_20using_20the_20windows_20api

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allocating_20arrays_20using_20the_20windows_20api [2018/03/31 13:19]
127.0.0.1 external edit
allocating_20arrays_20using_20the_20windows_20api [2018/04/17 15:01] (current)
tbest3112 Added syntax highlighting
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 //by Richard Russell, December 2006//\\ \\  You can allocate arrays, using **DIM**, either on BASIC'​s //heap// (global and PRIVATE arrays) or on the //stack// (LOCAL arrays). Using a combination of these will satisfy the needs of most programs. For example a skeleton program might be structured as follows:\\ \\  //by Richard Russell, December 2006//\\ \\  You can allocate arrays, using **DIM**, either on BASIC'​s //heap// (global and PRIVATE arrays) or on the //stack// (LOCAL arrays). Using a combination of these will satisfy the needs of most programs. For example a skeleton program might be structured as follows:\\ \\ 
 +<code bb4w>
         DIM globalarray1(...),​ globalarray2(...)         DIM globalarray1(...),​ globalarray2(...)
         REPEAT         REPEAT
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         REM .....         REM .....
         ENDPROC         ENDPROC
 +</​code>​
 \\  Here the memory occupied by arrays **localarray1()** and **localarray2()** is freed on exit from the first procedure and can be reused by **localarray3()** and **localarray4()** in the second procedure. This is a flexible arrangement and some combination of global and local arrays will usually suffice.\\ \\  However there may very rarely be situations which cannot satisfactorily be resolved using the capabilities of **DIM**. One is when the size of an array exceeds the amount of memory available to BBC BASIC for Windows (a total of 256 Megabytes). Another is when the memory occupied by the arrays cannot be allocated and freed in the required sequence, for example:\\ \\  \\  Here the memory occupied by arrays **localarray1()** and **localarray2()** is freed on exit from the first procedure and can be reused by **localarray3()** and **localarray4()** in the second procedure. This is a flexible arrangement and some combination of global and local arrays will usually suffice.\\ \\  However there may very rarely be situations which cannot satisfactorily be resolved using the capabilities of **DIM**. One is when the size of an array exceeds the amount of memory available to BBC BASIC for Windows (a total of 256 Megabytes). Another is when the memory occupied by the arrays cannot be allocated and freed in the required sequence, for example:\\ \\ 
  
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   - Destroy second array   - Destroy second array
 \\  Because LOCAL arrays are allocated on the //stack// they can only be destroyed in the reverse order from which they were created.\\ \\  In these cases it is possible to utilise the capabilities of the **Windows API** to allocate and free the memory used by arrays. By setting BASIC'​s internal pointers to the allocated memory such arrays can be used exactly as if they were declared using **DIM**, but the restrictions on size and sequence of creation and destruction are removed.\\ \\  The routines listed below illustrate how this can be achieved. For simplicity a separate routine is listed for 1-dimensional and 2-dimensional arrays. It should be relatively easy to see how this can be extended to arrays with more dimensions:​\\ \\  \\  Because LOCAL arrays are allocated on the //stack// they can only be destroyed in the reverse order from which they were created.\\ \\  In these cases it is possible to utilise the capabilities of the **Windows API** to allocate and free the memory used by arrays. By setting BASIC'​s internal pointers to the allocated memory such arrays can be used exactly as if they were declared using **DIM**, but the restrictions on size and sequence of creation and destruction are removed.\\ \\  The routines listed below illustrate how this can be achieved. For simplicity a separate routine is listed for 1-dimensional and 2-dimensional arrays. It should be relatively easy to see how this can be extended to arrays with more dimensions:​\\ \\ 
 +<code bb4w>
         DEF PROCdim1d(RETURN A(),S%,D1%)         DEF PROCdim1d(RETURN A(),S%,D1%)
         LOCAL A%         LOCAL A%
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         !^A() = 0         !^A() = 0
         ENDPROC         ENDPROC
 +</​code>​
 In each case the parameters supplied to the **PROCdim** procedure are the name of the array to be created, the size (in bytes) of each array element and the array'​s dimension(s). The element size should be specified as follows:\\ \\  In each case the parameters supplied to the **PROCdim** procedure are the name of the array to be created, the size (in bytes) of each array element and the array'​s dimension(s). The element size should be specified as follows:\\ \\ 
  
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 | **80-bit float** e.g. array()\\ | size=**10**+\\ | | **80-bit float** e.g. array()\\ | size=**10**+\\ |
  + BB4W version 6 only\\ \\  Note that if you free a **string** array using **PROCundim** you must first empty all the elements (set them to zero-length strings), for example:\\ \\   + BB4W version 6 only\\ \\  Note that if you free a **string** array using **PROCundim** you must first empty all the elements (set them to zero-length strings), for example:\\ \\ 
 +<code bb4w>
         array$() = ""​         array$() = ""​
         PROCundim(array$())         PROCundim(array$())
 +</​code>​
 You could use the above procedures to allocate and free arrays in a sequence which cannot otherwise be achieved:\\ \\  You could use the above procedures to allocate and free arrays in a sequence which cannot otherwise be achieved:\\ \\ 
 +<code bb4w>
         PROCdim1d(arr1%(),​4,​99)         PROCdim1d(arr1%(),​4,​99)
         arr1%(50) = 12345678         arr1%(50) = 12345678
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         PRINT arr2%(99)         PRINT arr2%(99)
         PROCundim(arr2%())         PROCundim(arr2%())
 +</​code>​
allocating_20arrays_20using_20the_20windows_20api.txt ยท Last modified: 2018/04/17 15:01 by tbest3112