Objects of type FILE can have a "position" that records how much of the file your program has already read. Many of the stdio functions depend on this position, and many change it as a side effect.
The result of ftell is the current position for a file identified by fp. If you record this result, you can later use it with fseek to return the file to this position.
In the current implementation, ftell simply uses a character count to represent the file position; this is the same number that would be recorded by fgetpos.### Returns
ftell returns the file position, if possible. If it cannot do this, it returns -1L. Failure occurs on streams that do not support positioning; the global errno indicates this condition with the value ESPIPE.
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**Authoritative source**: BUSMASTER DITA help source `ftell.dita`, compiled into `BUSMASTER.CHM` with the application.
