From QB64.org wiki
The LOF function is used to find the length of an OPEN file in bytes.
- totalBytes& = LOF([#]fileNumber)
- LOF returns the number of bytes in an OPENed designated fileNumber. File is empty if it returns 0.
- fileNumber is the number of the opened file. # is not required.
- Often used to determine the number of records in a RANDOM access file.
- Can also be used to avoid reading an empty file, which would create an error.
- LOF in QB64 can return up to 9 GB (9,223,372,036 bytes) file sizes.
Example: Finding the number of records in a RANDOM file using a TYPE variable.
OPEN file$ FOR RANDOM AS #1 LEN = LEN(Type_variable) NumRecords% = LOF(1) \ RecordLEN%