一、文件存取

与文件存储有关的系统调用

write
read
open
close
ioctl
lseek
fstat，stat，lstat

dup，dup2

#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
int main(){
    int fp;   
    mode_t fp_mode;
    fp_mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH;
    fp = open("test.txt", O_RDWR | O_CREAT, fp_mode);
    if ( fp != -1 ){
        printf("file created successfully!\n");
    }else{
        printf("failed!");
    }

    struct stat *buf = (struct stat*)malloc(sizeof(struct stat));
    if ( buf != NULL ){
        printf("buffer created successfully!\n");
    }else{
        printf("buffer created failed!\n");
    }
    fstat(fp, buf);
    if(buf->st_mode & S_IRUSR){
        printf("owner has read access!\n");
    }
    if(buf->st_mode & S_IWGRP){
        printf("group has write access!\n");
    }else{
        puts("group has no write access!");
    }
    close(fp);
    chmod("test.txt", 0664);
    stat("test.txt", buf);
    if(buf->st_mode & S_IWGRP){
        puts("group has write access!");
    }
    free(buf);



    char *dir = (char*)malloc(50);
    if(dir != NULL){
        getcwd(dir, 50);
        printf("current dir:%s\n", dir);
    }
    if(mkdir("test", 775) != -1){
        puts("dir created successfully!");
        chdir("test");
        puts("change workspace to test");
    }else{
        puts("couldn't create test dir!");
    }
    free(dir);
    return 0;
}

#include
#include
#include
#include
#include
#include
#define LENGTH 2000
void copy(char* oldfile, char* newfile);
int main(int argc, char* argv[])
{
    
    if(argc != 3){
        puts("invalid arguments!\n");
        return 1;
    }
    copy(argv[1], argv[2]);
    return 0;
}
void copy(char* oldfile, char* newfile)
{
    char buf[LENGTH];
    int f1,f2,i, j=0;
    mode_t f_mode = S_IRUSR | S_IWUSR | S_IRGRP;
    f1 = open(oldfile, O_RDONLY);
    if(f1!= -1){
        puts("file opened successfully!\n");
        i = read(f1, buf, LENGTH);
        if(i>0){
            printf("%s\n",buf);
        }
        f2 = open(newfile, O_WRONLY|O_CREAT, f_mode);
        if(f2 != -1){
            write(f2, buf, i);
        }else{
            puts("create file failed!\n");
        }
        puts("write completed!\n");
        close(f2);
    }else{
        puts("read file failed!");
        perror("file:");
    }
    close(f1);   
}

文件存取库函数

fopen，fclose
fread，fwrite
fflush
fseek
fgetc，getc，getchar
fputc， putc，putchar

fgets，gets

#include
#define SIZE 65535
#define LENGTH 1024
int main(){
    FILE *fp,*fp_copy;
    char buf[SIZE];
    fp = fopen("test.cpp","r");
    if(fp != NULL){
        puts("文件打开成功！");
        if(fread(buf, LENGTH, SIZE/LENGTH, fp) > 0){
            puts("文件读取成功！");
        }else{
            puts("文件读取失败!");
        }
    }else{
        perror("open file:");
        return 1;
    }
    fp_copy = fopen("test.txt", "w");
    if(fp_copy != NULL){
        puts("正在写入文件！");
        if(fwrite(buf, LENGTH, SIZE/LENGTH, fp_copy) >0){
            puts("文件写入成功！");
        }else{
            puts("写入失败！");
        }
    }
    if(fclose(fp)!= -1 && fclose(fp_copy) != -1){
        puts("文件关闭成功！");
    }else{
        perror("close file:");
        return 1;
    }
    return 0;
}

format input and output

printf, sprintf, fprintf

scanf, sscanf, fscanf

#include
#include
typedef struct{
    char name[20];
    char address[50];
    char stu_id[15];
} student;
int main(){
    student stu1;
    FILE *fp;
    if(creat("info.txt",0664) == -1){
        perror("创建文件失败！");
        return 1;
    }
    fp = fopen("info.txt","w");
    if(fp != NULL){
        fprintf(fp,":%s :%s :%s","xiaoming", "Beijing", "1010101");
        puts("输出信息成功!");
    }
    fclose(fp);
    fp = fopen("info.txt","r");
    fscanf(fp,":%s :%s :%s", stu1.name, stu1.address, stu1.stu_id);
    fclose(fp);
    printf("%s,%s,%s\n",stu1.name,stu1.address,stu1.stu_id);
    return 0;
}

file des position

fgetpos, fsetpos
ftell
rewind
freopen
setvbuf

remove

#include
#include
#include
#include
#define CTIME 3
typedef struct{
    int length;
    fpos_t fpos;
} pos_t;
int main(){
    pos_t pos[CTIME];
    FILE *fp;
    if(creat("temp",0664) == -1){
        perror("创建文件失败！");
        return 1;
    }
    fp = fopen("temp","rw+");
    for(int i = 0; i< CTIME; i++){
        fgetpos(fp, &pos[i].fpos);
        pos[i].length = fprintf(fp, "第%d次输出的数据！\n", i);
    }
    fflush(fp);
    printf("文件总长度:%d\n", ftell(fp));
    rewind(fp);
    char *buf;
    for(int i =0; i < CTIME ; i++){
        fsetpos(fp, &pos[i].fpos);
        buf = (char*)malloc(pos[i].length + 1);
        *(buf + pos[i].length +1) = '\0';
        fread(buf, pos[i].length, 1, fp);
        printf("%s",buf);
        free(buf);
    }
    fclose(fp);
    return 0;

}

error detect
- ferror
- feof
- clearerr
Streams and file descriptors
- fileno
  get fd from Stream
- fdopen
  open a stream from fd
file and directory maintence
- chmod
- chown
- link
- rmdir, mkdir
- chdir, getcwd

scan dir

opendir, closedir

readdir, telldir, seekdir

#include
#include
#include
#include
#include
#include
#include
#include
void scan_dir(char *dir, int depth);
int main(){
    puts("scan dir /boot\n");
    scan_dir("/boot",0);
    puts("scan completed!\n");
    return 0;
}
void scan_dir(char *dir, int depth){
    DIR *dp;
    struct dirent *entry;
    struct stat statbuf;
    if(dir==NULL){
        puts("you must input a dirname!");
        return;
    }
    if((dp = opendir(dir)) == NULL){
        printf("couldn't open the folder:%s\n", dir);
        return;
    }else{
        chdir(dir);
        while((entry = readdir(dp)) != NULL){
            lstat(entry->d_name, &statbuf);
            if(S_IFDIR & statbuf.st_mode){

                if(strcmp(entry->d_name,".")==0 || strcmp(entry->d_name,"..")==0){
                    continue;
                }
                printf("%*s%s/\n",depth, " ",entry->d_name);
                scan_dir(entry->d_name,depth+4);
            }else{
                printf("%*s%s\n", depth," ", entry->d_name);
            }

        }
        chdir("..");
        closedir(dp);
    }
}

error process
- strerror,perror

一、文件存取

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