This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
fgetc — get a byte from a stream
int fgetc(FILE * stream);
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.1‐2008 defers to the ISO C standard.
If the end-of-file indicator for the input stream pointed to by stream is not set and a next byte is present, the fgetc() function shall obtain the next byte as an unsigned char converted to an int, from the input stream pointed to by stream, and advance the associated file position indicator for the stream (if defined). Since fgetc() operates on bytes, reading a character consisting of multiple bytes (or ``a multi-byte character'') may require multiple calls to fgetc().
The fgetc() function may mark the last data access timestamp of the file associated with stream for update. The last data access timestamp shall be marked for update by the first successful execution of fgetc(), fgets(), fread(), fscanf(), getc(), getchar(), getdelim(), getline(), gets(), or scanf() using stream that returns data not supplied by a prior call to ungetc().
Upon successful completion, fgetc() shall return the next byte from the input stream pointed to by stream. If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-of-file indicator for the stream shall be set and fgetc() shall return EOF. If a read error occurs, the error indicator for the stream shall be set, fgetc() shall return EOF, and shall set errno to indicate the error.
The fgetc() function shall fail if data needs to be read and:
- The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the fgetc() operation.
- The file descriptor underlying stream is not a valid file descriptor open for reading.
- The read operation was terminated due to the receipt of a signal, and no data was transferred.
- A physical I/O error has occurred, or the process is in a background process group attempting to read from its controlling terminal, and either the calling thread is blocking SIGTTIN or the process is ignoring SIGTTIN or the process group of the process is orphaned. This error may also be generated for implementation-defined reasons.
The fgetc() function may fail if:
- The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream.
- Insufficient storage space is available.
The following sections are informative.
If the integer value returned by fgetc() is stored into a variable of type char and then compared against the integer constant EOF, the comparison may never succeed, because sign-extension of a variable of type char on widening to integer is implementation-defined.
The ferror() or feof() functions must be used to distinguish between an error condition and an end-of-file condition.
Section 2.5, Standard I/O Streams, feof(), ferror(), fgets(), fread(), fscanf(), getchar(), getc(), gets(), ungetc()
The Base Definitions volume of POSIX.1‐2008, <stdio.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
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