Basic operation of (C language) files

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File operations

The filename contains ： File path + File name trunk + File name suffix
Such as ：C:\Program Files (x86)\test.txt

Opening and closing of files

The file pointer

Buffer file system , The key concept is “ File type pointer ”, abbreviation “ The file pointer ”.

Each used file has a corresponding file information area in memory , It is used to store information about files （ Such as the name of the document , File status and current file location, etc ）.
This information is stored in a structure variable . The structure type is system declared , The name FILE

Open and close files

How files are used	meaning	If the specified file does not exist
“r”（ read-only ）	To enter data , Open an existing text file	error
“w”（ Just write ）	To output data , Open a text file	Create a new document
“a”（ Additional ）	Add data to a text file	Create a new document
“rb”（ read-only ）	To enter data , Open a binary file	error
“wb”（ Additional ）	To output data , Open a binary file	Create a new document
“ab”（ Reading and writing ）	Add data at the end of a binary file	error
“r+”（ Reading and writing ）	For reading and writing , Open a text file	error
“w+”（ Reading and writing ）	For reading and writing , Create a new file	Create a new document
“a+”（ Reading and writing ）	To open a file , Read and write at the end of the file	Create a new document
“rb+”（ Reading and writing ）	Open a binary file for reading and writing	error
“wb+”（ Reading and writing ）	For reading and writing , Create a new binary file	Create a new document
“ab+”（ Reading and writing ）	Open a binary file , Read and write at the end of the file	Create a new document

Such as ：

int main()
{
    
	FILE* pf = fopen("abc.txt", "r");// Read only open file 
	if (pf == NULL)
	{
    
		perror("fopen");
		return 1;
	}

	// Close file 
	fclose(pf);

	pf = NULL;

	return 0;
}

Sequential reading and writing of code

function	Function name	Apply to
Character input function	fgetc	All input streams
Character output function	fputc	All output streams
Text line input function	fgets	All input streams
Text line output function	fputs	All output streams
Format input function	fscanf	All input streams
Format output function	fprintf	All output streams
Binary input	fread	file
Binary output	fwrite	file

Random reading and writing of documents

fseelk

effect ： Locate the file pointer according to its position and offset （ Move the file pointer to the specified location ）

// Statement 
int fseek ( FILE * stream, long int offset, int origin );
					//offset origin  The number of bytes in .
										//origin  initial position .

#include <stdio.h>
int main()
{
    
	FILE* pf = fopen("test.txt", "wb");// Open a binary file 
	if (pf == NULL)
	{
    
		perror("fopen");
		exit(-1);
	}

	fputs("wo 1234 kenobi", pf);// write file 

	fseek(pf, 3, SEEK_SET);// Move the file pointer to the third position 

	fputs("jiao", pf);

	fclose(pf);// Close file 
	pf = NULL;

	return 0;
}

After operation test.txt It is shown as

wo jiao kenobi

ftell

effect ： Returns the offset of the file pointer from its starting position （ Get the current location of the file pointer ）

// Statement 
long int ftell ( FILE * stream );

usage ：

#include <stdio.h>
int main()
{
    
	FILE* pf = fopen("test.txt", "wb");// Open a binary file 
	if (pf == NULL)
	{
    
		perror("fopen");
		exit(-1);
	}

	fputs("wo 1234 kenobi", pf);
	int size = ftell(pf);
	printf("%d\n", size);

	fseek(pf, 3, SEEK_SET);
	size = ftell(pf);
	printf("%d\n", size);

	fclose(pf);
	pf = NULL;

	return 0;
}

function Pictured ：

rewind

effect ： Return the file pointer to the beginning of the file

// Statement 
void rewind ( FILE * stream );

usage ：

int main()
{
    
	FILE* pf = fopen("test.txt", "wb");// Open a binary file 
	if (pf == NULL)
	{
    
		perror("fopen");
		exit(-1);
	}

	fputs("wo 1234 kenobi", pf);	
	int size = ftell(pf);
	printf("%d\n", size);

	rewind(pf);

	size = ftell(pf);
	printf("%d\n", size);


	fclose(pf);
	pf = NULL;

	return 0;
}

function Pictured ：