c++读取文件

 

// read a file into memory
#include      // std::cout
#include       // std::ifstream

int main () {

  std::ifstream is ("test.txt", std::ifstream::binary);
  if (is) {
    // get length of file:
    is.seekg (0, is.end);
    int length = is.tellg();
    is.seekg (0, is.beg);

    char * buffer = new char [length];

    std::cout << "Reading " << length << " characters... ";
    // read data as a block:
    is.read (buffer,length);

    if (is)
      std::cout << "all characters read successfully.";
    else
      std::cout << "error: only " << is.gcount() << " could be read";
    is.close();

    // ...buffer contains the entire file...

    delete[] buffer;
  }
  return 0;
}

 

https://github.com/nedstarksbastard/FileReader/blob/master/CSVReader/main.cpp

//
//  main.cpp
//  CSVReader
//
//  Created by Fizi Yadav on 11/3/15.
//  Copyright © 2015 Fizi Yadav. All rights reserved.
//

#include 
#include 
#include 
#include 
#include 


size_t getFilesize(const char* filename) {
    /**
     * get the size of the file, Needed before calling mmap
     * @param filename a const char pointer.
     * @return file size in size_t
     */
    struct stat st;
    stat(filename, &st);
    return st.st_size;
}

size_t read(const char* filename){
    /**
     * read a file using mmap
     * @param filename a const char pointer.
     * @return file size read in size_t
     */
    // get file size.
    size_t filesize = getFilesize(filename);
    // open file
    int fd = open(filename, O_RDONLY, 0);
    if(fd == -1){
        std::cout<<"There was an opening the file\n";
        return 1;
    }
    // execute mmap
    void* mmappedData = mmap(NULL, filesize, PROT_READ, MAP_PRIVATE, fd, 0);
    if(mmappedData == NULL){
        std::cout<<"There was an error reading the file\n";
        return 1;
    }
    // write the mmapped data to stdout (= FD #1)
    write(1, mmappedData, filesize);
    // cleanup
    int rc = munmap(mmappedData, filesize);
    if(rc != 0){
        std::cout<<"There was an error removing the file mapping\n";
        return 1;
    }
    close(fd);
    return filesize;
    
}

int write(const char* filename){
    /**
     * write to a file
     * @param filename a const char pointer.
     * @return 0 or 1 to signify success or failure
     */
    
    int filedesc = open(filename, O_WRONLY | O_APPEND);
    if(filedesc < 0){
        std::cout<<"There was an opening the file\n";
        return 1;
    }
    
    if(write(filedesc,"This will be output to testfile.txt\n", 36) != 36)
    {
        std::cout<<"There was an error writing to testfile.txt\n";
        return 1;
    }
    
    return 0;
    
}

int main(int argc, const char * argv[]) {
    read("test.csv");
    return 0;
    
}