Updating a file using random access
For example, the Worker Type defined below creates 19-byte records that consist of three fields: Before your application opens a file for random access, it should declare all variables required to handle data from the file.
This includes user-defined types, which correspond to records in the file, as well as standard types for other variables that hold data related to processing a file opened for random access.
Then disks came along and now you can read any part of a file directly.
The File System Object model does not provide random file creation or access methods.
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Apart from the simplest of applications, most programs have to read or write files.
Acct# First Name Last Name Balance 0 "" "" 0.0 0 "" "" 0.0 0 "" "" 0.0 05 Joe Costanza 0.50 0 "" "" 0.0 0 "" "" 0.0 0 "" "" 0.0 19 Jason Bourne 58.00 0 "" "" 0.0 0 "" "" 0.0 42 Andy Der -15.12 0 "" "" 0.0 0 "" "" 0.0 I want to subtract an amount from balance from all the records that have a non zero account number and write the new updated balance to the file for those records.
I have even tried a single record without any while loop or if statement and it still does not work. loop: In case the plethora of differently-named file variables indicates that some version of your code tried to open the same file multiple times, reading from one version and writing to another: don't do that, and if you really must do it then flush the file between writing to it and trying to read from it.
cf Ptr = fopen("credit.dat", "rb "); fread(&client, sizeof(struct client Data), 1, cf Ptr); client.balance -= service Charge; fseek(cf Ptr,(Num - 1) * sizeof(struct client Data), SEEK_CUR); fwrite(&client, sizeof(struct client Data), 1, cf Ptr); I will assume that error checking on the function return values is 'not needed'; it should be there, but it will complicate things slightly.
Using file streams, we can randomly access binary files.
By random access, you can go to any position in the file as you wish (instead of going in a sequential order from the first character to the last).