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C miscellaneous lecture continued

2022-07-06 09:59:00 【Bright-SKY】

Catalog

Knowledge point 1【 Format read and write of file block 】（ important ）

1、fprintf Write operation of file

2、fscanf format Read operations

Knowledge point 2【 Random reading and writing of documents 】（ important ）

1、rewind Reset the file stream pointer

2、ftell Measure the number of bytes from the file reading and writing position to the beginning of the file

3、fseek Position pointer （ Reading and writing position ）

4、feof（） function Determine whether the file reaches the end of the file

Knowledge point 3【 File Encryptor 】

1、 Principle analysis

Project tips ：

Knowledge point 1【 Format read and write of file block 】（ important ）

fprintf( Write ) fscanf（ read ）

1、fprintf Write operation of file

void test06()
{
    HERO hero_buf[]={
   {" De Marcia ", 80, 60}, {" Tristana ", 40, 80}, {" Small method ",50, 90}};
    
    FILE *fp = NULL;
    fp = fopen("hero.txt", "w");
    if(fp == NULL)
    {
        perror("fopen");
        return;
    }

    int i=0;
    for ( i = 0; i < 3; i++)
    {
        fprintf(fp," full name :%s  defense :%d  attack :%d\n", \
        hero_buf[i].name,hero_buf[i].def,hero_buf[i].atk);
    }
    
    fclose(fp);
}

2、fscanf format Read operations

void test07()
{
    HERO hero_buf[3];
    memset(hero_buf, 0, sizeof(hero_buf));
    
    FILE *fp = NULL;
    fp = fopen("hero.txt", "r");
    if(fp == NULL)
    {
        perror("fopen");
        return;
    }

    int  i=0;
    for ( i = 0; i < 3; i++)
    {
        fscanf(fp," full name :%s  defense :%d  attack :%d\n", \
        hero_buf[i].name, &hero_buf[i].def,&hero_buf[i].atk);
    }

    for ( i = 0; i < 3; i++)
    {
        printf("%s %d %d\n", hero_buf[i].name, hero_buf[i].def,hero_buf[i].atk);
    }
    
    fclose(fp);
}

summary ：

Byte operation ：fgetc fputc

String manipulation ：fgets fputs

Block operation ：fread fwrite

Format operation ：fscanf fprintf

Knowledge point 2【 Random reading and writing of documents 】（ important ）

File default Sequential reading and writing

Introduction of knowledge points ：

void test01()
{
    FILE *fp = NULL;
    fp = fopen("c.txt", "w+");
    if(fp == NULL)
    {
        perror("fopen");
        return;
    }

    fputs("hello world", fp);
    fclose(fp);
    
    fp = fopen("c.txt", "r");

    char buf[1024]="";
    fgets(buf, sizeof(buf), fp);
    printf("buf=%s\n",buf);
    
    fclose(fp);
}

Resolve the above documents ： When the papers are finished Need to be closed file Then reopen the file Let the file stream pointer Point to the beginning of the file Let's change Next file read operation

Random reading and writing of documents ： Move the stream pointer of the file

rewind ftell fseek

1、rewind Reset the file stream pointer

void rewind(FILE *stream)

void test01()
{
    FILE *fp = NULL;
    fp = fopen("c.txt", "w+");
    if(fp == NULL)
    {
        perror("fopen");
        return;
    }

    fputs("hello world", fp);

    // Reset the file stream pointer 
    rewind(fp);

    char buf[1024]="";
    fgets(buf, sizeof(buf), fp);
    printf("buf=%s\n",buf);
    
    fclose(fp);
}

2、ftell Measure the number of bytes from the file reading and writing position to the beginning of the file

long ftell(FILE *stream);

3、fseek Position pointer （ Reading and writing position ）

int fseek(FILE *stream, long offset, int whence)

Case study 1： Pointer the file stream Navigate to the end of the file

fseek(fp, 0, 2);

Case study 2： File data Read to memory at one time

#include <stdlib.h>
#include <string.h>
void test02()
{
    FILE *fp = NULL;
    fp = fopen("a.txt", "r");
    if(fp == NULL)
    {
        perror("fopen");
        return;
    }

    // Get the total file size 
    fseek(fp, 0, 2);// Pointer the file stream   Navigate to the end of the file 
    long len = ftell(fp);// Get file size 
    rewind(fp);// Reset the file stream pointer （ Facilitate subsequent reading of file data ）
    printf("len = %ld\n", len);
    // Apply for space according to the total size of the file 
    unsigned char *data = NULL;
    data = (unsigned char *)calloc(1, len+1);
    fread(data, len, 1, fp);

    printf("%s\n", data);

    free(data);
    fclose(fp);
}

4、feof（） function Determine whether the file reaches the end of the file

EOF macro It can only be used for Wen Wen Wen file

feof function It can be used for Text document Binary

void test07()
{
	FILE *fp = NULL;
	fp = fopen("a.txt","r");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}

	//feof(fp)  Determine whether the file is   end  0： not finished     Not 0： End of the said 
	//while( feof(fp) == 0)// File not closed   Only then circulates 
	while(  !feof(fp) )
	{
		char ch = fgetc(fp);
		printf("%c", ch);
	}

	fclose(fp);
}

Running results ：

Knowledge point 3【 File Encryptor 】

1、 Principle analysis

The encryption process ：

The decryption process ：

main.c

#include<stdio.h>
#include"fun.h"
int main(int argc,char *argv[])
{
	while(1)
	{
		int cmd = 0;
		print_help();

		scanf("%d", &cmd);
		
		if(cmd == 1)
		{
			char src_file[31]="";
			char dst_file[31]="";
			char *file_data = NULL;
			unsigned long file_length = 0;
			unsigned int passwd = 0;

			//1、 Get source file   Destination file name ( Reference resources API Realization )
			get_file_name(dst_file, src_file);

			//2、 Get the source file name   Corresponding file   Content ( Reference resources API Realization )
			//char * read_src_file(unsigned long *file_length,char *src_file_name)
			file_data = read_src_file(&file_length, src_file);

			//3、 Get the password entered by the user （ Custom implementation ）
			printf(" Please enter your password :");
			scanf("%u", &passwd);

			//4、 Encrypt the contents of the file ( Reference resources API Realization )
			file_data = file_text_encrypt(file_data,file_length,passwd);
			//char * file_text_encrypt(char * src_file_text,unsigned long int length,unsigned int password)
			
			//5、 Yes, encrypted   The contents of the document   Save to   Destination file name 
			save_file(file_data, file_length,dst_file);
			//void save_file(char* text,unsigned long int length,char * file_name)
		}
		else if(cmd == 2)
		{
			char src_file[31]="";
			char dst_file[31]="";
			char *file_data = NULL;
			unsigned long file_length = 0;
			unsigned int passwd = 0;
			
			//1、 Get source file   Destination file name ( Reference resources API Realization )
			get_file_name(dst_file, src_file);
			//void get_file_name(char * dest_file_name,char * src_file_name)

			//2、 Get the source file name   Corresponding file   Content ( Reference resources API Realization )
			file_data = read_src_file(&file_length, src_file);
			//char * read_src_file(unsigned long int *file_length,char *src_file_name)
			
			//3、 Get the password entered by the user （ Custom implementation ）
			printf(" Please enter your password :");
			scanf("%u", &passwd);

			//4、 Decrypt file contents ( Reference resources API Realization )
			file_data = file_text_decrypt(file_data, file_length,passwd);
			//char * file_text_decrypt(char * src_file_text,unsigned long int length,unsigned int password)
			
			//5、 Yes, encrypted   The contents of the document   Save to   Destination file name 
			save_file(file_data, file_length,dst_file);
			//void save_file(char* text,unsigned long int length,char * file_name)
		}
		else if(cmd == 3)
		{
			break;
		}
		else
		{
			printf(" Please enter a correct option \n");
		}

	}
	
	return 0;
}

fun.c

#include<stdio.h>
#include<stdlib.h>
void print_help(void)
{
	printf("**********1: Encrypt file **************\n");
	printf("**********2: Decrypt files **************\n");
	printf("**********3: Exit procedure **************\n");
}
void get_file_name(char * dest_file_name,char * src_file_name)
{
	printf(" Please enter the name of your source file (30 Characters ):");
	scanf("%s", src_file_name);
	printf(" Please enter the name of your destination file (30 Characters ):");
	scanf("%s", dest_file_name);
	return;
}

char * read_src_file(unsigned long *file_length,char *src_file_name)
{
	char *data = NULL;
	FILE *fp = NULL;
	fp = fopen(src_file_name,"r");
	if(fp == NULL)
	{
		perror("fopen");
		return NULL;
	}

	// Get the total length of the file 
	// Pointer the file stream   location   To the file   The tail 
	fseek(fp,0,2);
	// Get file length 
	*file_length = ftell(fp);
	// Reset the file stream pointer 
	rewind(fp);


	// according to   The length of the file   apply   Heap space 
	data = (char *)calloc(1,*file_length);
	if(data == NULL)
	{
		perror("calloc");
		return NULL;
	}

	// Disposable   Read file contents 
	fread(data, *file_length,1,fp);

    fclose(fp);
	// Put the first address of the space   return 
	return data;
}
char * file_text_encrypt(char * src_file_text,unsigned long int length,unsigned int password)
{
	int i=0;
	for(i=0;i<length;i++)
	{
		src_file_text[i] += password;// Encryption process 
	}

	return src_file_text;
}

void save_file(char* text,unsigned long int length,char * file_name)
{
	FILE *fp = NULL;
	fp = fopen(file_name, "w");
	if(fp == NULL)
	{
		perror("fopen");
		return;
	}

	// take data The data is saved to   In file 
	fwrite(text, length, 1, fp);

	fclose(fp);
	
	// Release text Point to heap space 
	if(text != NULL)
	{
		free(text);
		text =NULL;
	}

	printf(" Saved successfully !\n");
	return;
}

char * file_text_decrypt(char * src_file_text,unsigned long int length,unsigned int password)
{
	int i=0;
	for(i=0;i<length;i++)
	{
		src_file_text[i] -= password;// Decryption process 
	}

	return src_file_text;
}

fun.h

#ifndef __FUN_H__
#define __FUN_H__

extern void print_help(void);
extern void get_file_name(char * dest_file_name,char * src_file_name);
extern char * read_src_file(unsigned long *file_length,char *src_file_name);
extern char * file_text_encrypt(char * src_file_text,unsigned long int length,unsigned int password);

extern void save_file(char* text,unsigned long int length,char * file_name);
#endif

Project tips ：

1： Open the file in binary mode for reading and writing .

2： Method of measuring file size ：

1） use fseek() Locate the stream pointer to the end of the file .

2） use ftell() The function measures the position of the stream pointer, that is, the size of the file .

3： Read the contents of the document ：

1） According to the size of the file, use malloc Apply for memory space to save the read content

2） When reading file data, read from the beginning of the file （rewind（））.

Detailed design API Design reference ：

1) Get the names of source and destination files from the keyboard

/**************************************************************************/

// The functionality : obtain Name of destination file and source file

// Parameters ： src_file_name: Source file name character array first address .

// dest_file_name: The first address of the name character array of the destination file

/**************************************************************************/

void get_file_name(char * dest_file_name,char * src_file_name)

2) Read from the file

/**************************************************************************/

// The functionality : Read file contents

// Parameters ：file_length: Integer pointer , The number of bytes saved in this address .

// src_file_name: File name , Read from this file .

// Return value : Read the first address of the string

// Measure the size of the file in this function , and malloc Space , Then read out the contents of the file and return , Read the first address of the character array

/**************************************************************************/

char * read_src_file(unsigned long int *file_length,char *src_file_name)

3) Character array encryption

/**************************************************************************/

// The functionality : Encrypted string

// Parameters ：

// src_file_text: The string to encrypt . length: Length of string

// password: Encrypted password

// Return value : The first address of the encrypted string

// Encryption principle add password

/**************************************************************************/

char * file_text_encrypt(char * src_file_text,unsigned long int length,unsigned int password)

4) Decrypt string

/**************************************************************************/

// The functionality : Decrypt string

// Parameters ：

// src_file_text: String to decrypt . length: Length of string

// password: Decrypt password

// Return value : The first address of the decrypted string

// thought ; Subtract each element in the array password Assign values to yourself .

/**************************************************************************/

char * file_text_decrypt(char * src_file_text,unsigned long int length,unsigned int password)

5) Save the file

/**************************************************************************/

// The functionality : Save the string to the destination file

// Parameters ：

// text: The first address of the string to be saved

// file_name : Name of the destination file

// length: Length of string

// thought ： Pass in the first address of the character array, the size of the array and the name of the saved file , You can save the array to a file

/**************************************************************************/

void save_file(char* text,unsigned long int length,char * file_name)

6) Print file information

/**************************************************************************/

// The functionality : Print help

/**************************************************************************/

void print_help()

{

printf("********1: Encrypt file ***********\n");

printf("********2: Decrypt files ***********\n");

printf("********3: Exit procedure ***********\n");

}