Acorn computer econet level 2/3 User Manual
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Contents
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Using the pointerThe next step is to point to the particular byte in the file that youwant to read or write to. The pointer keyword is PTR#.EXAMPLEPTR#X=1000This means: in the file with channel X, point to byte number1000. The byte number will be increased by 1 each time a byte isread or written. When a file is opened, the pointer points to byte0.Reading and writingNow you can read or write to the contents of the byte you havepointed to. The keywords are BGET# (to read a byte) andBPUT# (to write a byte).EXAMPLESNEXTLETTER%=BGET#XThis means: into the variable NEXTLETTER% put the contentsof the byte currently pointed to in the file with channel X.BPUT#X,32This means: into the byte currently pointed to in the file withchannel X, put the number 32.When you are writing to a file, you can increase its size bypointing beyond the current last byte. For example, if youOPENUP a file 20 bytes long and then point to byte 100, usingPTR#, the file will be extended to 100 bytes. The extra bytesinserted will be zeros.41 |
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