c++ - 流 >> 读取最后一行两次

Question

我正在尝试解析 /proc/partitions 文件。

major minor  #blocks  name

   8        0  976762584 sda
   8        1   99998720 sda1
   8        2          1 sda2
   8        3  103561216 sda3
   8        4  291514368 sda4
   8        5    1998848 sda5

这是我机器中的/proc/partitions 文件。

#include <boost/cstdint.hpp>
#include <fstream>
#include <boost/algorithm/string/trim.hpp>
#include <boost/format.hpp>

int main(){
  std::ifstream proc_partitions_stream("/proc/partitions");
  boost::int32_t disc_partition_line_count = -2; //-1 for headers, -1 for the empty line
  //so counter is 0 when it tries to read the real entries
  while(!proc_partitions_stream.fail()){
    if(disc_partition_line_count >= 0){
      boost::uint16_t   major, minor;
      boost::uint64_t   blocks;
      std::string   label;
      proc_partitions_stream >> major >> minor >> blocks >> label;
      std::cout << boost::format("%1% %2% %3% %4%") % major % minor % blocks % label << std::endl;
      boost::algorithm::trim(label);      
    }else{
      std::string line;
      std::getline(proc_partitions_stream, line);
    }
    ++disc_partition_line_count;
  }
    return 0;
}

但是它读取最后一行两次这是程序

8 0 976762584 [sda]
8 1 99998720 [sda1]
8 2 1 [sda2]
8 3 103561216 [sda3]
8 4 291514368 [sda4]
8 5 1998848 [sda5]
8 5 1998848 [] << read the last line TWICE but didn't read the label

Answer 1

因为你的 while 循环条件是错误的，你在阅读之前测试失败，你应该在阅读之后测试失败。更好的方法是测试 getline 的返回值。