C Standard Library -<stdio.h>

Introduction

stdio .hThe header file defines three variable types, a number of macros, and various functions for performing input and output.

<stdio.h>It is a header file in the C standard library that defines various functions and types for handling files and standard input/output streams.

Library variables

The following are the variable types defined in the header file stdio.h:

Serial Number	Variables & Description
1	size_t This is an unsigned integer type, which issizeofResult of the keyword, indicating the size of an object.
2	FILE File stream type, an object type suitable for storing file stream information.
3	fpos_t File position type, an object type suitable for storing any position within a file.

Library macros

The following are the macros defined in the header file stdio.h:

Serial Number	Macros & Description
1	NULL This macro is the value of a null pointer constant.
2	_IOFBF、_IOLBFand _IONBF These macros expand to integer constant expressions with specific values and are suitable forsetvbufThe third parameter of the function.
3	BUFSIZ This macro is an integer that representssetbufThe buffer size used by the function.
4	EOF This macro is a negative integer indicating that the end of the file has been reached.
5	FOPEN_MAX This macro is an integer that represents the number of files that the system can open simultaneously.
6	FILENAME_MAX This macro is an integer that represents the maximum length of a filename that a character array can store. If the implementation has no restrictions, this value should be the recommended maximum.
7	L_tmpnam This macro is an integer that represents the maximum length of a character array that can store a temporary filename created by the tmpnam function.
8	SEEK_CUR、SEEK_ENDandSEEK_SET These macros are infseekused in functions to position at different locations within a file.
9	TMP_MAX This macro is the maximum number of unique filenames that the tmpnam function can generate.
10	stderr、stdinandstdout These macros are pointers to the FILE type, corresponding to the standard error, standard input, and standard output streams, respectively.

Library functions

The following are the functions defined in the header file stdio.h:

To better understand the functions, study them in the following sequence, because the file created in the first function will be used in subsequent functions.

Serial Number	Functions & Description
1	int fclose(FILE *stream) Closes the stream stream. Flushes all buffers.
2	void clearerr(FILE *stream) Clears the end-of-file and error indicators for the given stream stream.
3	int feof(FILE *stream) Tests the end-of-file indicator for the given stream stream.
4	int ferror(FILE *stream) Tests the error indicator for the given stream stream.
5	int fflush(FILE *stream) Flushes the output buffer of the stream stream.
6	int fgetpos(FILE stream, fpos_t pos) Gets the current file position of the stream stream and writes it to pos.
7	FILE fopen(const char filename, const char *mode) Opens the file pointed to by filename using the given mode mode.
8	size_t fread(void ptr, size_t size, size_t nmemb, FILE stream) Reads data from the given stream stream into the array pointed to by ptr.
9	FILE freopen(const char filename, const char mode, FILE stream) Associates a new filename filename with the given open stream stream, while closing the old file in the stream.
10	int fseek(FILE *stream, long int offset, int whence) Sets the file position of the stream stream to the given offset offset, parameteroffsetMeans from a givenwhenceThe number of bytes for position lookup.
11	int fsetpos(FILE stream, const fpos_t pos) Sets the file position of the given stream stream to the given position. The parameterposis the position given by the function fgetpos.
12	long int ftell(FILE *stream) Returns the current file position of the given stream stream.
13	size_t fwrite(const void ptr, size_t size, size_t nmemb, FILE stream) Writes data from the array pointed to by ptr to the given stream stream.
14	int remove(const char *filename) Deletes the given filename filename so that it can no longer be accessed.
15	int rename(const char old_filename, const char new_filename) Change the filename pointed to by old_filename to new_filename.
16	void rewind(FILE *stream) Sets the file position to the beginning of the file of the given stream stream.
17	void setbuf(FILE stream, char buffer) Defines how the stream stream should be buffered.
18	int setvbuf(FILE stream, char buffer, int mode, size_t size) Another function that defines how the stream stream should be buffered.
19	FILE *tmpfile(void) Create a temporary file in binary update mode (wb+).
20	char tmpnam(char str) Generates and returns a valid temporary filename that did not exist previously.
21	int fprintf(FILE stream, const char format, ...) Sends formatted output to the stream stream.
22	int printf(const char *format, ...) Sends formatted output to standard output stdout.
23	int sprintf(char str, const char format, ...) Send formatted output to a string.
24	int vfprintf(FILE stream, const char format, va_list arg) Sends formatted output to the stream stream using an argument list.
25	int vprintf(const char *format, va_list arg) Sends formatted output to standard output stdout using an argument list.
26	int vsprintf(char str, const char format, va_list arg) Sends formatted output to a string using an argument list.
27	int fscanf(FILE stream, const char format, ...) Reads formatted input from the stream stream.
28	int scanf(const char *format, ...) Reads formatted input from standard input stdin.
29	int sscanf(const char str, const char format, ...) Read formatted input from a string.
30	int fgetc(FILE *stream) Gets the next character (an unsigned character) from the specified stream stream and moves the position indicator forward.
31	char fgets(char str, int n, FILE *stream) Reads a line from the specified stream stream and stores it in the string pointed to by str. When(n-1)characters are read, or when a newline character is read, or when the end of the file is reached, it stops, whichever comes first.
32	int fputc(int char, FILE *stream) Writes the character (an unsigned character) specified by the argument char to the specified stream stream and moves the position indicator forward.
33	int fputs(const char str, FILE stream) Writes the string to the specified stream stream, excluding the null character.
34	int getc(FILE *stream) Gets the next character (an unsigned character) from the specified stream stream and moves the position indicator forward.
35	int getchar(void) Gets a character (an unsigned character) from standard input stdin.
36	char gets(char str) Reads a line from standard input stdin and stores it in the string pointed to by str. It stops when a newline character is read or when the end of the file is reached, depending on the situation.
37	int putc(int char, FILE *stream) Writes the character (an unsigned character) specified by the argument char to the specified stream stream and moves the position indicator forward.
38	int putchar(int char) Writes the character (an unsigned character) specified by the argument char to standard output stdout.
39	int puts(const char *str) Writes a string to standard output stdout, up to but not including the null character. A newline character is appended to the output.
40	int ungetc(int char, FILE *stream) Pushes the character char (an unsigned character) back onto the specified stream stream so that it is the next character to be read.
41	void perror(const char *str) Outputs a descriptive error message to standard error stderr. First the string str is output, followed by a colon, then a space.
42	int snprintf(char str, size_t size, const char format, ...) Format string into str.

Example

The following are some usage<stdio.h>Examples of functions in:

Opening and closing files:

Example

#include <stdio.h>

int main() {
FILE *file = fopen("example.txt", "r");
if (file == NULL) {
perror("Error opening file");
return 1;
}
// Perform file operations
fclose(file);
return 0;
}

Read file contents:

Example

#include <stdio.h>

int main() {
FILE *file = fopen("example.txt", "r");
if (file == NULL) {
perror("Error opening file");
return 1;
}

char buffer[256];
while (fgets(buffer, sizeof(buffer), file) != NULL) {
printf("%s", buffer);
}

fclose(file);
return 0;
}

Write file content:

Example

#include <stdio.h>

int main() {
FILE *file = fopen("example.txt", "w");
if (file == NULL) {
perror("Error opening file");
return 1;
}

fprintf(file, "Hello, World!\n");

fclose(file);
return 0;
}

Notes

UsagefopenAfter opening a file, be sure to usefcloseCloses the file to avoid file resource leaks.
UsagefgetsWhen reading strings, be sure to pay attention to the size of the buffer to avoid buffer overflow.
Usageprintf、scanfWhen using functions, be sure to pay attention to the correctness of the format string to avoid undefined behavior.

By understanding and using<stdio.h>The functions provided make it convenient to perform file and standard input/output operations, and to write more robust and flexible C programs.

other extensions