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Device file ： In the operating system, every input connected to the host 、 The output device is treated as a file , Put their input 、 Output is equivalent to disk text Reading and writing of documents

（ The purpose of the buffer is ： Improve access efficiency Disk life ）

2、 Classification of disk files

Physically All disk files are Binary storage , In bytes Sequential storage .

logically Document classification ：

text file ： File based on character encoding

Binary ： File based on value encoding

summary ：

3、 The file pointer

Be careful ： Don't care about beginners FILE The details of the It only needs Will use FILE Just define pointer variables ：FILE *fp=NULL;

Knowledge point 2【 Operation file's Library function 】

1、fopen Open file

#include <stdio.h>
FILE *fopen(const char *path, const char *mode);

mode：

read-write permission ：r read w Write a Additional + Can read but write t text file （ Omit ） b Binary

r: With read-only Way to open a file

file non-existent return NULL;

file There is return The file pointer , Perform subsequent read operations

w: With Just write Way to open a file

file does not exist , Create this file with the specified file name , And open the file ;

If document There is , Empty The contents of the document , Open file , And then write ;

If the file cannot be opened （ For example, the file is read-only ）, return NULL

a: With Additional Way to open a file

file does not exist , Create this file with the specified file name ( Same as w)

If the file exists , From the file Ending Write operation

2、 Close file fclose

#include <stdio.h>
int fclose(FILE *fp);

3、 Read and write one character at a time

（1）、 Byte read operation fgetc

int fgetc(FILE *stream)// Read operations

Return value ：

With t The way ： Read to the end of the file and return EOF

With b The way ： Read to the end of the file , Use feof( The back can speak ）

void test03()
{
	char buf[128]="";
	int i=0;
	FILE *fp = NULL;
	//1、 Use fopen Open a file   Get file pointer 
	fp = fopen("a.txt", "r");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}

	//2、 Operations on files  fgetc
	while(1)
	{
		//fgetc Call once   Read a byte 
		buf[i] = fgetc(fp);
		if(buf[i] == EOF)//EOF The table has been aligned to the end of the file 
		{
			break;
		}
		i++;
	}
	printf("buf=%s\n", buf);

	//3、 Close file 
	fclose(fp);
}

Running results ： In advance, Local establish a.txt The contents of the document by hello file

（2）、 Byte write operation fputc

int fputc(int c, FILE *stream)// Write operations 
fputc  take  c  The value of is written as  stream

Return value ：

If the output is successful , Returns the byte value of the output ;

If the output fails , Returns a EOF

EOF Is in stdio.h Symbols defined in the document

void test04()
{
	char buf[128]="";
	int i=0;
	FILE * fp =NULL;
	fp = fopen("b.txt", "w");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}

	// Use fputc Write the data of the file 
	printf(" Please enter the string to write to the file :");
	fgets(buf,sizeof(buf),stdin);// Will get line breaks 
	buf[strlen(buf)-1] = 0;// Remove the newline character of keyboard input 
	
	// The string buf The elements in   Write to the file one by one 
	while(buf[i] != '\0')
	{
		fputc(buf[i], fp);
		i++;
	}

	fclose(fp);
}

Running results ：

routine ： From a file ( text file ) Read all information in , Write to another file

void test05()
{
	// demand ： from a.txt Read file contents   Write to b.txt
	FILE *fp1 =NULL;
	FILE *fp2 =NULL;
	
	// Open as read-only a.txt
	fp1 = fopen("a.txt","r");
	if(fp1 == NULL)
	{
		perror("fopen");
		return;
	}

	// Open in write only mode b.txt
	fp2 = fopen("b.txt","w");
	if(fp2 == NULL)
	{
		perror("fopen");
		return;
	}


	// from fp1 in    Every read   byte   Write to fp2 in 
	while(1)
	{
		char ch;
		// read 
		ch = fgetc(fp1);
		if(ch == EOF)// Read to the end of the file 
			break;

		// Write 
		fputc(ch,fp2);

	}
	fclose(fp1);
	fclose(fp2);
	return;
}

4、 Read and write one string at a time

（1）、 Use fgets Get string from file

char *fgets(char *s, int size, FILE *stream)

from stream Read characters from the file referred to , Stop reading when you encounter a newline character or the end of the file .

Or read size-1 Stop reading bytes , After the read content, a \0, As the end of a string

Return value ：

success : Return the address of the first element of the read string

Failure ： return NULL

Get the data of one line of the file ：

void test07()
{
	char buf[128]="";
	FILE *fp = NULL;
	char *path = "c.txt";
	fp = fopen(path, "r");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}

	//err  Open a file named "path"  instead of path The file name that points to "c.txt"
	//fp = fopen("path", "r");
	//fp = fopen("c.txt", "r");
	
	while(fgets(buf,sizeof(buf),fp))
	{
		printf("%s\n", buf);
	}

	fclose(fp);
}

Running results ：

（2）、 Use fputs Write a string to the file

int fputs(const char *s, FILE *stream);

Case study ：

void test06()
{
	// Pointer array 
	char *buf[]={" The bright moon in front of the window \n"," Suspected frost on the ground \n"," look at the bright moon \n"," Bow your head and think of your hometown "};
	int n = sizeof(buf)/sizeof(buf[0]);
	FILE *fp = NULL;
	int i=0;

	fp = fopen("c.txt", "w");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}
	
	for(i=0;i<n; i++)
	{
		fputs(buf[i], fp);
	}

	fclose(fp);
}

Running results ：

5、 Reading and writing of file blocks fread fwrite Memory data as is Output to disk

1、 Use fwrite take Data blocks Write to a file

typedef struct
{
	char name[16];// full name 
	int deff;// defense 
	int atk;// attack 
}HERO;

void test08()
{
	HERO hero[]={
		{" De Marcia ",80, 60},
		{" Blind monk ",90, 80},
		{" Small method ",40, 85},
		{" Tristana ",50, 90}
	};
	int n = sizeof(hero)/sizeof(hero[0]);

	FILE *fp = NULL;
	fp = fopen("hero.txt", "w");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}
	
	//fwrite  Put the data in memory as it is   Output to   In file 
	// Data written to a file   Inconvenient   User view   however   Does not affect the   Program reading 
	fwrite(hero, sizeof(HERO), n, fp);

	fclose(fp);
}

Running results ：

2、 Use fread From file Read Data blocks

The whole block number is returned Less than one piece It doesn't count

Case study ：

void test09()
{
	HERO hero[4];
	int i=0;
	FILE *fp = NULL;
	fp = fopen("hero.txt", "r");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}
	
	fread(hero,sizeof(HERO), 4, fp);
	
	for(i=0;i<4;i++)
	{
		//printf(" Hero name :《%s》, defense :《%d》, damage :《%d》\n", \
			hero[i].name,hero[i].deff,hero[i].atk);
		printf(" Hero name :《%s》, defense :《%d》, damage :《%d》\n", \
			(hero+i)->name,(hero+i)->deff,(hero+i)->atk);
	}


	fclose(fp);
}

Running results ：