c读写文件实例

#include <stdio.h>                                                
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>

int main(int argc,char *argv[]){
    //读取文件路径
    char *filepath = argv[1];
    //保存文件路径
    char *savepath = argv[2];
    int fd,savefd,size;
    char buffer[1024];
    struct stat fstat;
    mode_t mode;

    //打开文件
    fd = open(filepath,O_RDWR);
    if((stat(filepath,&fstat)) < 0){
        perror("run fstat error");
    }
    //判断文件类型
    mode = fstat.st_mode;
    if(S_ISREG(mode)){
        printf("Type:regular file\n");
    }else if(S_ISDIR(mode)){
        printf("Type:direcory\n");
        return 0;
    }
    if(fd != -1){
        //在文件不存在新建时生效，使用8进制设置新建文件的权限
        savefd = open(savepath,O_RDWR|O_CREAT,0777);
        //读取文件内容
        while((size=read(fd,buffer,sizeof(buffer))) > 0){
            printf("%s",buffer);
            //写文件
            if(savefd != -1){
                //注意：读取多少，则写入多少,此处为size
                if((write(savefd,buffer,size)) == -1){
                    perror("Write error!");
                }
            }
        }
    }
    exit(0);
}                                                                     

实例二：

/*
**功能：文件读写实例
*/
#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<unistd.h>
#include<sys/stat.h>
#include<sys/types.h>
#include<sys/file.h>
#include<string.h>
#include "lockset.h"
void lock_set(int fd,int type);
int main(int argc,char *argv[]){
	
	char *input = argv[1];
	char *filepath = argv[2];

	//注意一定需要先清零，否则读取的时候就会多读出无效的字符
	char rdbuff[100] = {0};
	
	printf("input:%s\n",input);
	printf("filepath:%s\n",filepath);
	int opfd,wrsize,rdsize,len;
	opfd = open(filepath,O_RDWR|O_CREAT,0777);
	if(opfd == -1){
		perror("Open Error!\n");
		exit(1);
	}
	//加上写入锁
	lock_set(opfd,F_WRLCK);
	if((wrsize = write(opfd,input,strlen(input))) == strlen(input)){
		printf("Write Success!\n");
	}
        //等待输入字符，起到暂停的作用
	getchar();

	//解锁
	lock_set(opfd,F_UNLCK);
	getchar();

	//加上读取锁
	lock_set(opfd,F_RDLCK);
	lseek(opfd,0,SEEK_SET);
	//当读取的rdsize == 0时表示读取完,-1表示读取失败
	if((rdsize = read(opfd,rdbuff,sizeof(rdbuff))) > 0){
		printf("Read:%s\n",rdbuff);
	}else{
		printf("Read Error!\n");
	}
	//解锁
	lock_set(opfd,F_UNLCK);
	getchar();
	close(opfd);
	exit(0);
}

lockset.h头文件

void lock_set(int fd,int type){

	struct flock lock;
	lock.l_whence = SEEK_SET;
	lock.l_start = 0;
	lock.l_len = 0;
	while(1){
		lock.l_type = type;
		if((fcntl(fd,F_SETLK,&lock)) ==0){
			if(lock.l_type == F_RDLCK){
				printf("read lock set by %d\n",getpid());
			}else if(lock.l_type == F_WRLCK){
				printf("write lock set by %d\n",getpid());
			}else if(lock.l_type == F_UNLCK){
				printf("release lock set by %d\n",getpid());
			}
			return;
		}
		fcntl(fd,F_GETLK,&lock);
		if(lock.l_type != F_UNLCK){
			if(lock.l_type == F_RDLCK){
				printf("Read lock already set by %d\n",lock.l_pid);
			}else if(lock.l_type == F_WRLCK){
				printf("Write lock already set by %d\n",lock.l_pid);
			}
			getchar();
		}
	}
}