c++实现读写文件

本程序主要利用mmap函数利用映射的方式实现文件的读写，可以在此基础上改动实现read，write方式

CFile.h

#include <iostream>#include <cstdio>#include <unistd.h>#include <sys/mman.h>#include <fcntl.h>#include <cstring>#include <string>#include <sys/stat.h>#include <sys/types.h>class CFile{public:CFile(const std::string& filename);    virtual ~CFile();bool openFile(const char* filemode);    int getFd() { return fd;}int getFileSize();bool writeFile(const std::string& data);void closeFile();bool unlinkFile();std::string getFileName(){ return filename;}bool checkFile();bool reName(const std::string& newname);void readFile(void* buf, int size, int offset);void* getMapPtr() { return mapptr;}void syncFile(int size) {msync((char*)mapptr+mapsize-size, size, MS_ASYNC);}int getFileCreatTime();private:   bool unmapFile(){if(mapptr){if(munmap(mapptr, maxsize) !=0){return false;}}return true;    }bool mmapFile(){mapptr = mmap(0, maxsize, PROT_READ|PROT_WRITE, MAP_SHARED,fd, 0);if(mapptr == NULL){std::cout<< "map file err\n"; return false;}return true;    }off_t getPosition(){return lseek(fd, 0, SEEK_END);}private:int fd;FILE* file;void* mapptr;unsigned long int offset;size_t mapsize, maxsize;const std::string filename;    CFile(const CFile&);CFile& operator=(const CFile&);};CFile::CFile(const std::string& filename):filename(filename),mapsize(0),maxsize(65535),file(NULL){}CFile::~CFile(){if(file)closeFile();}void CFile::closeFile(){if(fd <0) return;if (!unmapFile()) {std::cout << "unmap err\n";}       if(fd >0) close(fd);fd = -1;  file = NULL;}bool CFile::openFile(const char* filemode) //"at+"{if(!checkFile()){std::cout << "file not exists\n";return false;}file = fopen(filename.c_str(), filemode);if(file == NULL){std::cout << "open file err\n";return false;}else{fd = fileno(file);mapsize = getPosition();}return true; }int CFile::getFileSize(){struct stat filestat;fstat(fd, &filestat);return filestat.st_size;// long int curpos,length;// curpos = ftell(file);// fseek(file, 0L,SEEK_END);// length = ftell(file);// fseek(file,curpos, SEEK_SET);// return length;}bool CFile::writeFile(const std::string& data){size_t datasize = data.size();int fileLen = mapsize;int offset = datasize + fileLen;if(offset >= maxsize){    closeFile();reName(filename+std::string(".bk"));if(!checkFile())return false;}if(fd < 0){std::cout<< "no open the file\n"; return false;}if(ftruncate(fd, offset) < 0){return false;}mmapFile();char *ptr = reinterpret_cast<char*>(mapptr);memcpy(ptr+fileLen, data.c_str(), datasize);mapsize = offset;return true;  }bool CFile::unlinkFile(){if(!checkFile()){return false;}closeFile();return remove(filename.c_str())==0?true:false;}bool CFile::checkFile(){if(access(filename.c_str(), F_OK)==0)return true;else{int fd = open(filename.c_str(), O_CREAT);if(fd < 0){std::cout << "create file err\n";return false;}close(fd);}return true;}bool CFile::reName(const std::string& newname){if(rename(filename.c_str(), newname.c_str())==0)return true;elsereturn false;}void CFile::readFile(void* buf, int size, int offs){if(!checkFile()){std::cout << "read file err\n";return;}int length = getFileSize();if( offs > length){std::cout << "offset number too big\n";return;}else{int readavail = 0;    if(size + offs > length){            readavail = length - offs;}elsereadavail = size;void* ptr = mmap(NULL, readavail, PROT_READ | PROT_WRITE, MAP_SHARED,                           fd, 0);char *p = reinterpret_cast<char*>(ptr);memcpy(buf, (void*)(p+offs), readavail);}}int CFile::getFileCreatTime(){struct stat info;stat(filename.c_str(), &info);return info.st_ctime;}

Test.cpp

#include "CFile.h"int main(int argc, char *argv[]){    std::string filename("./log");CFile *cFile = new CFile(filename);// cFile->openFile("a+");// char buf[20] = {'\0'};// cFile->readFile(buf, 10, 3);// std::cout <<buf <<"\n";// cFile->closeFile();cFile->openFile("at+");std::string writestr("ABCDEFGHIJKLMNOPQRSTUVWXYZ\n");cFile->writeFile(writestr);std::string writestr2("sdgagagaergrefzrew\n");cFile->writeFile(writestr2);cFile->syncFile(writestr.size() + writestr2.size());// std::cout << cFile->getFileSize() << "\n";cFile->closeFile();//const std::string newname("./clog");//cFile->reName(newname);//cFile->unlinkFile();    return 0;}