ftell, ftello - return a file offset in a stream
long ftell(FILE *stream);
[CX] off_t ftello(FILE *stream);
[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
The ftell() function shall obtain the current value of the file-position indicator for the stream pointed to by stream.
The ftell() function shall not change the setting of errno if successful.
[CX] The ftello() function shall be equivalent to ftell(), except that the return value is of type off_t and the ftello() function may change the setting of errno if successful.
Upon successful completion, ftell() [CX] and ftello() shall return the current value of the file-position indicator for the stream measured in bytes from the beginning of the file.
Otherwise, ftell() and ftello() shall return -1, and set errno to indicate the error.
The ftell() [CX] and ftello() functions shall fail if:
- [CX] The file descriptor underlying stream is not an open file descriptor.
- [CX] For ftell(), the current file offset cannot be represented correctly in an object of type long.
- [CX] For ftello(), the current file offset cannot be represented correctly in an object of type off_t.
- [CX] The file descriptor underlying stream is associated with a pipe, FIFO, or socket.
Standard I/O Streams, fgetpos, fopen, fseek, lseek
First released in Issue 1. Derived from Issue 1 of the SVID.
Large File Summit extensions are added.
Extensions beyond the ISO C standard are marked.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
The ftello() function is added.
The [EOVERFLOW] error conditions are added.
An additional [ESPIPE] error condition is added for sockets.
POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0204 , XSH/TC1-2008/0205 , XSH/TC1-2008/0206 , XSH/TC1-2008/0207 , and XSH/TC1-2008/0208  are applied.
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