缓冲区的相关理解以及概念、
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模拟C语言库的缓冲区和文件相关封装的实现：
Mystdio.c文件：
#define FILE_MODE 0666 _FILE* _fopen(const char *filename, const char *flag) { assert(filename); assert(flag); int mode = 0; size_t fd = -1; //判断打开方式，模拟w、a、r if(strcmp(flag,"w") == 0) { //设置文件权限 mode = (O_CREAT|O_WRONLY|O_TRUNC); //打开文件 fd = open(filename,mode,FILE_MODE); } else if(strcmp(flag,"a") == 0) { mode = (O_CREAT|O_WRONLY|O_APPEND); fd = open(filename,mode,FILE_MODE); } else if(strcmp(flag,"r") == 0) { mode = O_RDONLY; fd = open(filename,mode); } else { return NULL; } //有可能文件都没打开 if(fd == -1) { return NULL; } //把fd放到_FILE结构体对象中 _FILE* fp = (_FILE*)malloc(sizeof(_FILE)); if(fp == NULL) { perror("malloc fail"); return NULL; } fp->fileno = fd; fp->flag = FLUSH_LINE;//行刷新 fp->out_pos = 0; return fp; } int _fwrite(_FILE *fp, const char *s, int len) { //将s拷贝到缓冲区中 memcpy(&fp->outbuffer[fp->out_pos],s,len); fp->out_pos += len; //判断刷新方式 if(fp->flag & FLUSH_NOW) { //立即刷新 write(fp->fileno,fp->outbuffer,fp->out_pos); fp->out_pos = 0; } else if(fp->flag & FLUSH_LINE) { //行刷新 if(fp->outbuffer[fp->out_pos] == '\n') { write(fp->fileno,fp->outbuffer,fp->out_pos); fp->out_pos = 0; } else { return len; } } else if(fp->flag & FLUSH_ALL) { //全缓冲 if(fp->out_pos == SIZE) { write(fp->fileno,fp->outbuffer,fp->out_pos); fp->out_pos = 0; } else { return len; } } } void _fflush(_FILE *fp) { if(fp->out_pos > 0) { write(fp->fileno,fp->outbuffer,fp->out_pos); fp->out_pos = 0; } } void _fclose(_FILE *fp) { if(fp == NULL) { return ; } _fflush(fp); close(fp->fileno); free(fp); }
Mystdio.h文件：
#ifndef __MYSTDIO_H__ #define __MYSTDIO_H__ #include<string.h> #define SIZE 1024 #define FLUSH_NOW 1 #define FLUSH_LINE 2 #define FLUSH_ALL 4 typedef struct IO_FILE { int fileno;//文件描述符 int in_pos;//缓冲区已经写了多少 char inbuffer[SIZE];//输入缓冲区 int out_pos;//缓冲区已经写了多少 char outbuffer[SIZE];//输出缓冲区 int flag;//刷新方式 }_FILE; void _fflush(_FILE *fp); _FILE* _fopen(const char *filename, const char *flag); int _fwrite(_FILE *fp, const char *s, int len); void _fclose(_FILE *fp); #endif
测试main.c文件：
#include "Mystdio.h" int main() { _FILE *fp = _fopen("test.txt","a"); if(fp == NULL) { return 1; } const char *message = "I miss you\n"; _fwrite(fp,message,strlen(message)); _fflush(fp); _fclose(fp); return 0; }
