C, c + + file operations-file concepts and file writing

Files are used to persist data

Persistent: Data does not disappear after power failure. Next time you add, you can read

Properties of the file:

Filename

Path

Length (measured in bytes)

Content

Read-only/read-write

fopen Open a file

Fclose closing files

Fwrite writing data

Fread closing files

Steps to save data to a file

1) fopen Open File

FILE *fopen (const char * filename, const char * mode);

Mode uses WB, writes binary

2) fwrite Write data

size_t fwrite (const void * buf, size_t size, size_t count, FILE * stream);

BUF the data to write

Size is always 1

Count length

Stream fopen the created pointer

3) fclose Close file

Simple example of writing data

#include <stdio.h>intMain () {//Define file name    Const Char* filename ="C:/aaa.txt"; //Open the file, the system will create a file based on the specified path and file nameFILE * fp = fopen (filename,"WB"); //Determines whether the file pointer is empty to determine whether the file was created successfully    if(fp = =NULL) {printf ("failed to open file!\n"); return-1; }          CharBuf[] ="Hello"; //Write DataFwrite (BUF,1,5, FP); intA =0x12345678; Fwrite (&a,1,4, FP);        Fclose (FP); return 0;} 

Write Data in detail

I. Writing data to an array

The code is as follows

#include <stdio.h>#include<string.h>intMain () {//Define file name    Const Char* filename ="C:/aaa.txt"; //Open the file, the system will create a file based on the specified path and file nameFILE * fp = fopen (filename,"WB"); //Determines whether the file pointer is empty to determine whether the file was created successfully    if(fp = =NULL) {printf ("failed to open file!\n"); return-1; }          intbuf[4] = {0xa001,0xb002,0xc003,0xd004};
         for(inti =0; I <4; i++)    {        Chartext[ -]; //convert int type data to character typesprintf (Text,"%d,", Buf[i]); Fwrite (text,1, strlen (text), FP);        } fclose (FP); return 0;} 

Two. Specify format to save decimals

#include <stdio.h>#include<string.h>intMain () {//Define file name    Const Char* filename ="C:/aaa.txt"; //Open the file, the system will create a file based on the specified path and file nameFILE * fp = fopen (filename,"WB"); //Determines whether the file pointer is empty to determine whether the file was created successfully    if(fp = =NULL) {printf ("failed to open file!\n"); return-1; }         DoubleA =3/4.0; Chartext[ -]; //keep two decimal placessprintf (Text,"%.2LF", a); Fwrite (text,1, strlen (text), FP);        Fclose (FP); return 0;}

Three. Writing a string

Two ways to store strings

char buf [+] = "Hello";

Method 1: Store by actual effective length (using the Strlen function inside the string.h to get the string specific length)

Fwrite (buf, 1, strlen (BUF), FP);

Mode 2: Write by fixed length

Fwrite (BUF, 1, (+), FP);

(More space occupied)

#include <stdio.h>#include<string.h>intMain () {//Define file name    Const Char* filename ="C:/aaa.txt"; //Open the file, the system will create a file based on the specified path and file nameFILE * fp = fopen (filename,"WB"); //Determines whether the file pointer is empty to determine whether the file was created successfully    if(fp = =NULL) {printf ("failed to open file!\n"); return-1; }    Charbuf[ -] ="Hello"; //fwrite (Buf,1,strlen (BUF), FP);

  Fwrite (buf,1,

return 0 ;

}

Four. Writing to a struct

#include <stdio.h>#include<string.h>structstudent{intID; Chargender; Charname[ -];};intMain () {//Define file name    Const Char* filename ="C:/aaa.txt"; //Open the file, the system will create a file based on the specified path and file nameFILE * fp = fopen (filename,"WB"); //Determines whether the file pointer is empty to determine whether the file was created successfully    if(fp = =NULL) {printf ("failed to open file!\n"); return-1; } Student someone= {61031,'M',"Noname"}; //fwrite (&someone, 1, sizeof (someone), FP);fwrite (&someone.gender,1,1, FP); Fwrite (&someone.id,1,4, FP); Fwrite (&someone.gender,1, -, FP);    Fclose (FP); return 0;}

fopen (filename, "WB");

When the parameter is WB, the content will overwrite

When the parameter is AB, the written content is appended to the back

C, c + + file operations-file concepts and file writing