fgetc - get a byte from a stream
int fgetc(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.
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().
[CX] 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, [CX] and shall set errno to indicate the error.
The fgetc() function shall fail if data needs to be read and:
- [CX] The O_NONBLOCK flag is set for the file descriptor underlying stream and the thread would be delayed in the fgetc() operation.
- [CX] The file descriptor underlying stream is not a valid file descriptor open for reading.
- [CX] The read operation was terminated due to the receipt of a signal, and no data was transferred.
- [CX] 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.
- [CX] The file is a regular file and an attempt was made to read at or beyond the offset maximum associated with the corresponding stream.
The fgetc() function may fail if:
- [CX] Insufficient storage space is available.
- [CX] A request was made of a nonexistent device, or the request was outside the capabilities of the device.
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.
Standard I/O Streams, feof, ferror, fgets, fread, fscanf, getchar, getc, gets, ungetc
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 [EIO] and [EOVERFLOW] mandatory error conditions are added.
The [ENOMEM] and [ENXIO] optional error conditions are added.
The following changes are made for alignment with the ISO/IEC 9899:1999 standard:
The DESCRIPTION is updated to clarify the behavior when the end-of-file indicator for the input stream is not set.
The RETURN VALUE section is updated to note that the error indicator shall be set for the stream.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/32 is applied, updating the [EAGAIN] error in the ERRORS section from "the process would be delayed" to "the thread would be delayed".
Austin Group Interpretation 1003.1-2001 #051 is applied, updating the list of functions that mark the last data access timestamp for update.
POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0129  and XSH/TC1-2008/0130  are applied.
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