The processing and application of C language to documents

because c Language is a language that deals directly with the kernel , At the same time as a highly portable programming language , So in many cases we can use c Language for programming , Corresponding with the use , The use of documents is inevitable , Here I mainly talk about my understanding of file processing and application

The first is to understand the file , In the process of file processing, the path of the most important file first , The main consideration in daily use is window Interrupt location , But if you use linux The system needs to consider the absolute path and relative path of its files , It's far away , In a word, path is a very important thing , You need to write the correct path in the program .

Next is the file type , There is no emphasis here , Text files are basically used in daily life

Finally, the file name , The corresponding file name can be found in the path , So there is no emphasis

So, on the basis of knowing the basic knowledge of the file , You can learn further backwards

stay c How to create a file in the language

Here you can use the same operation as opening a file fopen() function , This function does not require the use of additional header files , You only need to use normal #include<stdio.h> that will do

So when it comes to this , Let's talk about the normal file operations .

fgetc() Generally, it is to get all the characters in a file ,fclose() It is usually used to close files

fopen( file name , Use file mode );  // The file name is a string , Double quotation marks are required for use ,
fegrtc( The file pointer ）   // Read a character from the file pointed to by the pointer
fputc(ch,fp)    // Put the character variable ch writes fp In the file that you point to
 

So here you can use it to operate on the information in the file

If I am window I want to input a file , You can do this

#include <stdio.h>
int main()
{
     FILE*p; // Set a file pointer 

     char ch; // Define a character variable 

     if((p=fopen("test.txt","w"))==NULL) // Open one called test Text file for , In a write only way , When     When something goes wrong , That is, the return value is NULL when , Output error message 
     {
            printf("ERROR");

           exit(0); // Close all files , Terminate the program in progress 
      }

      for(;ch!='\n';) // Input ch Know to enter spaces .
      {
            scanf("%c",&ch);
             fputc(ch,p); // The character ch write in p The file pointed to 
      } 
fclose(p);// Close file 
}

This is a simple file processing operation found on the Internet , But there is a problem with this , For example, in file operation , There won't be a single line of everything in and out , Generally, it will be wrapped , Then note that the fifteen lines have judgment on the line feed operation , Therefore, it is not possible to operate by line when inputting , At this time, the best way is to read by bytes and input by bytes

This will be mentioned later .

There's one more thing to note , In this case, all previous information will be deleted , Then get the newly entered information , If you want to add to it rather than copy, you'd better add to the eighth line w Make changes to become a that will do , For specific reasons, please refer to the table above

At this time, the writing of the string is finished , Then you can copy the file , This operation is also easy to understand , Generally, you can use this for backup , Then we need the above fegrtc() and fputc() These two methods

The specific implementation idea is to copy the string in the previous file and then copy the contents to another file

So it's easy to handle

#include <stdio.h>
int main()
{
	FILE*p1,*p2;    // Set up 2 A file pointer 
	
	char filename[30],filename1[30],ch;  // Set up 2 An array of characters is used to enter the file name 
	
	printf(" Please enter the file name to copy \n"); 
	
	gets(filename);      // Input file name 
	
	printf(" Please enter the copied file name ：\n");
	
	gets(filename1);     // Input file name 
	
	if((p1=fopen(filename,"rb"))==NULL)  // Open the copied file 
	{
		printf("ERROR");
		
		exit(0);
	}
	if((p2=fopen(filename1,"wb"))==NULL) // Write the file name to be copied 
	{
		printf("ERROR");
		
		exit(0);
	}
	
	while(!feof(p1))    // Use a function to check whether the file ends 
	{
		ch=fgetc(p1);   // Read each p1 Bytes in the file pointed to , hold ch Write to p2 Point to the file , without p2 file , Will create a filename1 Character array named file 
		
		fputc(ch,p2);
	} 
	
	printf(" Replication success "); 
	
	fclose(p1);   // After use , To avoid unnecessary operations interfering with reading and writing , To close the file , That is, disconnect the file pointer from the file 
	fclose(p2);
	
	
	
}

 feof( The file pointer )   // When the file ends, it returns non 0 value , Returns... When the file is not finished 0

This can also be used for file processing , Notice that it will return... When it is not processed 0, But at the end of processing, it will return non 0 value , Then you only need to use it when copying while(!feof(fp)) Just judge

Because I have just said the reason , So when I want to read and write a file more accurately , The best method is still binary reading and writing .

The following three functions are most commonly used in binary reading and writing fopen(),fread(),fwrite()

So with the above foundation , It is easy to understand these three functions .

because fopen() I've already said , So here we mainly talk about fread(),fwrite() These two functions

fread() Four parameters are required

Let's first look at the defined function

size_t fread(void * ptr,size_t size,size_t nmemb,FILE * stream);

fread() Used to read data from the file stream . Parameters stream Pointer to an open file , Parameters ptr Point to the data space to be read , Number of characters read parameter size*nmemb To decide .Fread() Will return the actually read nmemb number , If this value is greater than the parameter nmemb Come small , It means that the end of the file may be read or an error may occur , You have to use feof() or ferror() To decide what happens .

  for instance

	
#include<stdio.h>
#define nmemb 3
struct test
{
char name[20];
int size;
}s[nmemb];
main()
{
FILE * stream;
int i;
stream = fopen("bearst","r");
fread(s,sizeof(struct test),nmemb,stream);
fclose(stream);
for(i=0;i<nmemb;i++)
printf("name[%d]=%-20s:size[%d]=%d/n",i,s[i].name,i,s[i].size);
}

Its return value is

name[0]=Linux! size[0]=6
name[1]=FreeBSD! size[1]=8
name[2]=Windows2000 size[2]=11

Note that the return value here is not fixed , The details should be related to the actual situation  

fwrite() Similar to it , The parameters in the defined function are the same

So just look at the examples

 

#include<stdio.h>
#define set_s (x,y) {strcoy(s[x].name,y);s[x].size=strlen(y);}
#define nmemb 3
struct test
{
char name[20];
int size;
}s[nmemb];
main()
{
FILE * stream;
set_s(0,"Linux!");
set_s(1,"FreeBSD!");
set_s(2,"Windows2000.");
stream=fopen("/tmp/fwrite","w");
fwrite(s,sizeof(struct test),nmemb,stream);
fclose(stream);
}