システム呼び出しファイルの読み書き操作

ファイルからデータを読み込む
1コード

#include
#include
#include
#include
#include

int main(void)
{
    int fd = -1,i;
    ssize_t size =-1;
    char buf[10];   
    char filename[] = "/root/test.txt"; //      

    fd = open(filename,O_RDONLY); //        
    if(-1==fd)
    {   
            printf("Open file %s failuer,fd:%d
",filename,fd);
               return -1;
    }
    else  printf("Open file %s success,fd:%d
",filename,fd);
  
    //      ，          
    while(size)
    {   
       //        ，10       10   ，               
        size = read(fd,buf,10);       
        if(-1==size)
        {   
            close(fd);
            printf("Read file %s error occurs
",filename);
            return -1;
        }else{
            if(size>0)
            {   
                printf("read %d bytes:",size);
                printf("\"");
                for(i =0;i

2運転

[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# ./test
Open file /root/test.txt success,fd:3
read 10 bytes:"fhdjslfgdh"
read 10 bytes:"jdskfjsdhj"
read 10 bytes:"gfdlfgdfg;"
read 10 bytes:"dfgflk
fsd"
read 10 bytes:"klfjsfjdlf"
read 10 bytes:"jdk
nfjsdk"
read 1 bytes:"
"
reach the end of file
[root@localhost test]# cat /root/test.txt
fhdjslfgdhjdskfjsdhjgfdlfgdfg;dfgflk
fsdklfjsfjdlfjdk
nfjsdk

ファイルへのデータの書き込み
1コード

#include
#include
#include
#include
#include
#include

int main(void)
{
    int fd = -1,i;
    ssize_t size =-1;
    int input =0;
    
    char buf[] = "boys and girls
 hi,children!";  
    char filename[] = "test.txt";
    
    fd = open(filename,O_RDWR|O_APPEND);  
    if(-1==fd)
    {   
        printf("Open file %s faliluer 
",filename );
    }else{
        printf("Open file %s success 
,=",filename );
    }   
    size = write(fd,buf,strlen(buf));  
    printf("write %d bytes to file %s
",size,filename);
    
    close(fd);
    return 0;
}

2運転

[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# touch test.txt
[root@localhost test]# ./test
Open file test.txt success
,=write 28 bytes to file test.txt