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The C programming language provides many standard library functions for file input and output.These functions make up the bulk of the C standard library header <stdio.h>. [1] The functionality descends from a "portable I/O package" written by Mike Lesk at Bell Labs in the early 1970s, [2] and officially became part of the Unix operating system in Version 7.
Alignment specification (_Alignas specifier, _Alignof operator, aligned_alloc function, <stdalign.h> header) The _Noreturn function specifier and the <stdnoreturn.h> header; Type-generic expressions using the _Generic keyword. For example, the following macro cbrt(x) translates to cbrtl(x), cbrt(x) or cbrtf(x) depending on the type of x:
The tie::AnyDBM_File function associates a hash with a file. [2] C library POSIX definition ... a and + and returns a file pointer used with fgets, fputs and fclose. mode
The C library functions, including the ISO C standard ones, are widely used by programs, and are regarded as if they were not only an implementation of something in the C language, but also de facto part of the operating system interface. Unix-like operating systems generally cannot function if the C library is erased.
The formatting placeholders in scanf are more or less the same as that in printf, its reverse function.As in printf, the POSIX extension n$ is defined. [2]There are rarely constants (i.e., characters that are not formatting placeholders) in a format string, mainly because a program is usually not designed to read known data, although scanf does accept these if explicitly specified.
The C standard library function fgets() is best avoided in binary mode because any file not written with the Unix newline convention will be misread. Also, in text mode, any file not written with the system's native newline sequence (such as a file created on a Unix system, then copied to a Windows system) will be misread as well.
Off-by-one errors are common in using the C library because it is not consistent with respect to whether one needs to subtract 1 byte – functions like fgets() and strncpy will never write past the length given them (fgets() subtracts 1 itself, and only retrieves (length − 1) bytes), whereas others, like strncat will write past the length given them.
Some implementations read lines with the function readlinebuffer() which does not impose any line length limits if system memory suffices. Other implementations read lines with the function fgets(). This function requires a fixed buffer. For these implementations, the buffer is often sized according to the POSIX macro LINE_MAX.