stdio.h
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Overview
The keyword stdio.h in C is a header file. The reason why we use stdio.h in C is that this header file imports different variables, macros, and functions to perform input and output operations. To perform input and output operations in our C program, we need to import the stdio.h header file into our program.
Introduction
The stdio.h is one of the most commonly used header file in C. This file enables us to use the input and output functionality in C. As stdio.h contains more than 40 functions that are used to perform input and output operations, we get a lot of different ways to get and display data in C.
What is stdio.h in C?
The file stdio.h is a built-in header file in C. The acronym stdio stands for Standard Input and Output. This header file contains 3 variables, multiple function definitions, and multiple macro definitions. These variables, functions, and macros are related to the input and output operations in C.
Syntax to Include stdio.h in C
#include is a preprocessor directory in C. This keyword is used to include (or import) a header file into our program.
Use of stdio.h
The stdio.h header file allows us to perform input and output operations in C. The functions like printf() and scanf() are used to display output and take input from a user, respectively. This library allows us to communicate with users easily.
The stdio.h library uses streams to communicate with physical devices. A stream is a communication channel between a program and the physical input and output devices. For example, a standard input (stdin) is a stream used to read input data from a keyboard.
Stdio.h Library Variables
There are 3 variables (or types) in the stdio.h library. These are:
| S. No. | Variable Name | Variable Description |
|---|---|---|
| 1 | FILE | It is a data object that stores the information about controlling streams. |
| 2 | size_t | It is an unsigned integral data type. It is the return type of the sizeof operator. |
| 3 | fpos_t | It is a data object that is used to represent any position in a file. |
Stdio.h Library Macros
The name given to a small piece of code is called a macro. Following are some of the commonly used stdio.h library's macros:
| S. No. | Macro Name | Macro Description |
|---|---|---|
| 1 | EOF | It stands for End Of File. It contains a negative integer that indicates the end of a file |
| 2 | NULL | It represents a Null Pointer (a pointer that does not point to anything) |
| 3 | FOPEN_MAX | It contains an integer that represents the number of files that can be opened simultaneously |
| 4 | FILENAME_MAX | It contains an integer that represents the maximum size (in bytes) of a filename string |
| 5 | L_tmpnam | It contains an integer that represents the maximum size of a temporary filename string |
| 6 | BUFSIZ | It contains an integer that represents the buffer size used by setbuf function |
| 7 | TMP_MAX | It contains an integer that represents the maximum unique filenames the tmpnam function can generate |
| 8 | stdin, stdout, stderr | These macros stand for standard input, standard output, and standard error, respectively. They are pointers to the FILE object |
| 9 | _IOFBF, _IOLBF, _IONBF | These macros stand for Input Output Fully Buffered, Line Buffered, and Unbuffered, respectively. They specify the mode for file buffering |
| 10 | SEEK_END, SEEK_SET, SEEK_CUR | These macros are used to locate different file positions |
Stdio.h Library Functions
There are several stdio.h library functions in C. These functions are used to perform different input and output functions.
Following are the stdio.h functions:
| S. No. | Function Name | Function Description |
|---|---|---|
| 1 | printf | Displays data to stdout |
| 2 | scanf | Reads input data from stdin |
| 3 | fprintf | Displays data to the stream |
| 4 | fscanf | Reads input data from the stream |
| 5 | vprintf | Displays data from an argument list to stdout |
| 6 | vscanf | Reads input data into an argument list |
| 7 | sprintf | Writes output to a string |
| 8 | sscanf | Reads data from a string input |
| 9 | snprintf | Writes output to a buffer of given size |
| 10 | vsnprintf | Displays data from an argument list to a buffer of given size |
| 11 | vsprintf | Displays data from an argument list to a string |
| 12 | vsscanf | Reads data from a string into an argument list |
| 13 | vfprintf | Displays data from an argument list to the stream |
| 14 | vfscanf | Reads input data from the stream to an argument list |
| 15 | tmpnam | Creates a new temporary file |
| 16 | tmpfile | Opens a temporary file in binary update mode |
| 17 | rename | Renames the given file |
| 18 | remove | Deletes the given file |
| 19 | fopen | Opens the given file |
| 20 | fclose | Closes an open file |
| 21 | fflush | Flushes the output of the given stream |
| 22 | setbuf | Specifies the buffer of a stream |
| 23 | setvbuf | Update the buffer of a stream |
| 24 | freopen | Restarts the stream to open a new file or open the existing file with a different access mode |
| 25 | fgetc | Fetches the next character from the given stream |
| 26 | fputc | Writes a new character to the given stream |
| 27 | fgets | Fetches a line (string) from the given stream |
| 28 | fputs | Writes a new string to the given stream |
| 29 | getc | Fetches the next character from the given stream |
| 30 | gets | Fetches a string from stdin |
| 31 | getchar | Fetches the next character from stdin |
| 32 | putchar | Writes a new character to stdout |
| 33 | putc | Writes a new character to the given stream |
| 34 | puts | Writes a new string to stdout |
| 35 | ungetc | Pushes a character in the given stream in order to read the next character |
| 36 | fread | Reads data from a stream |
| 37 | fwrite | Writes data to a stream |
| 38 | rewind | Sets the file position of a given stream to the beginning |
| 39 | fgetpos | Fetches the current file position in a given stream |
| 40 | fseek | Advances the position of a given stream to the specified number of bytes |
| 41 | fsetpos | Sets the position of a given stream to the position given by fgetpos function |
| 42 | ftell | Fetches the current file position in a given stream |
| 43 | ferror | Checks error indicators for a given stream |
| 44 | feof | Checks the EOF indicator for a given stream |
| 45 | perror | Displays the error message |
| 46 | clearerr | Deletes the error indicators for a given stream |
Let us look at a simple example to understand a couple of commonly used stdio.h functions.
Output:
In the above example, we defined a string str and declared a variable extracted_value. Then, we used the sscanf() function (it comes from the stdio.h header file) to extract (or read) all the characters from the string str and store them in the variable extracted_value. Finally, we used another stdio.h function, i.e. printf(), to print the value stored in extracted_value.
Conclusion
- The keyword stdio.h is a header file in C.
- The stdio.h library imports variables, functions, and macros into our program.
- The variables, functions, and macros imported by stdio.h are used to perform input and output operations.
- printf() and scanf() are two of the most commonly used stdio.h functions.