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69 lines
2.9 KiB
Markdown
69 lines
2.9 KiB
Markdown
The [CVI](CVI) function decodes a 2-byte [STRING](STRING) generated by [MKI$](MKI$) (or read from a file) to [INTEGER](INTEGER) numeric values.
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## Syntax
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> result% = [CVI](CVI)(stringData$)
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## Description
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* *CV* functions ([CVD](CVD), [CVS](CVS), [CVI](CVI), [CVL](CVL), [CVDMBF](CVDMBF), [CVSMBF](CVSMBF)) are used to convert values encoded by *MK$* functions ([MKD$](MKD$), [MKS$](MKS$), [MKI$](MKI$), [MKL$](MKL$), [MKDMBF$](MKDMBF$), [MKSMBF$](MKSMBF$)).
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* **QB64** has [_CV](_CV) and [_MK$](_MK$) functions which can also deal with extended [Data types](Data-types).
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* [INTEGER](INTEGER) values can range from -32768 to 32767.
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* Doesn't return [_UNSIGNED](_UNSIGNED) values.
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## Example(s)
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*Example 1:*
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```vb
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FIELD #1, 2 AS N$, 12 AS B$...
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GET #1 'GET does not need a position or variable with successive FIELD buffer reads
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Y = CVI(N$)
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```
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> *Explanation:* Reads a field from file #1, and converts the first two bytes (N$) into an integer number assigned to the variable Y.
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> Since the representation of an integer number can use up to 5 ASCII characters (five bytes), writing to a file using [MKI$](MKI$) conversion, and then reading back with the [CVI](CVI) conversion can save up to 3 bytes of storage space.
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How CVI converts the ASCII code values created by the MKI$ function.
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```vb
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SCREEN 12
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DIM Q AS STRING * 1
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Q = CHR$(34)
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' create Print using templates to align the values returned
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tmp1$ = "1st character code = ### * 1 = ### "
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tmp2$ = "2nd character code = ### * 256 = ##### "
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tmp3$ = " & "
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tmp4$ = " CVI Total = ##### "
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DO
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COLOR 14: LOCATE 13, 20: INPUT "Enter an Integer from 1 to 32767(0 quits): ", number%
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IF number% < 1 THEN EXIT DO
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CLS
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ASCII$ = MKI$(number%) ' create the 2 byte character string
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COLOR 11
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_PRINTSTRING (152, 240), "MKI$ creates 2 byte ASCII string: " + Q + ASCII$ + Q ' displays character(s)
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asc1% = ASC(ASCII$) ' find the ASCII code values of each character
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asc2% = ASC(ASCII$, 2) ' **QB64** allows ASC to read specific characters in a string
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LOCATE 18, 20: PRINT USING tmp1$; asc1%; asc1%
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LOCATE 19, 20: PRINT USING tmp2$; asc2%; asc2% * 256
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LOCATE 20, 20: PRINT USING tmp3$; "-----"
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LOCATE 21, 20: PRINT USING tmp4$; asc1% + (256 * asc2%)
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LOOP
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SYSTEM
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```
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> *Explanation:* All [ASCII](ASCII) characters can be displayed using [_PRINTSTRING](_PRINTSTRING) . The routine gets the [ASCII](ASCII) code, which is the actual value needed by [CVI](CVI). The first byte code is always between 0 and 255. The second byte can return 0 thru 127 and CVI multiplies that value by 256. This proves that you cannot just feed a string number value to [CVI](CVI) and get the result desired. ("90" gets decoded to 12345).
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## See Also
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* [MKD$](MKD$), [MKI$](MKI$), [MKS$](MKS$), [MKL$](MKL$), [MKDMBF$](MKDMBF$), [MKSMBF$](MKSMBF$)
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* [CVS](CVS), [CVD](CVD), [CVL](CVL), [CVSMBF](CVSMBF), [CVDMBF](CVDMBF)
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* [_CV](_CV), [_MK$](_MK$)
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