C Language and Libraries Help (clang.hlp) (Table of Contents; Topic list)
_tell
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─────Run-Time Library───────────────────────────────────────────────────────
 
     The _tell function gets the current position of the file pointer
     (if any) associated with the <handle> argument. The position is
     expressed as the number of bytes from the beginning of the file.
 
     Return Value
 
     A return value of -1L indicates an error, and errno is set to
     EBADF to indicate an invalid file-handle argument. On devices
     incapable of seeking, the return value is undefined.
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