当它击中eof时std :: getline投掷

Question

std::getline当它获得一个时抛出异常eof.这就是我的表现.

std::ifstream stream;
stream.exceptions(std::ifstream::failbit|std::ifstream::badbit);
try{
  stream.open(_file.c_str(), std::ios_base::in);
}catch(std::ifstream::failure e){
  std::cout << "Failed to open file " << _file.c_str() << " for reading" << std::endl;
}
while(!stream.eof()){
  std::string buffer = "";
  std::getline(stream, buffer);
  //process buffer
  //I do also need to maintain state while parsing
}

在上面的代码getline中抛出异常,因为它获得了eof 如何处理这种情况？

编辑

std::string buffer = "";
while(std::getline(stream, buffer)){
    //also causes getline to hit eof and throw
}

Answer 1

您可以在代码的最开头激活流的异常处理:

stream.exceptions(std::ifstream::failbit|std::ifstream::badbit);

现在,如果提取格式化数据(如浮点值,整数或字符串)将失败,它将设置failbit:

eofbit    indicates that an input operation reached the end of an 
          input sequence;
failbit   indicates that an input operation failed to read the expected 
          characters, or that an output operation failed to generate the 
          desired characters.

虽然getline(stream,buffer)确实会设置eofbitif到达文件的末尾,但它也会设置failbit,因为无法提取所需的字符(一行).

在循环周围包装另一个try-catch-block或禁用failbit异常.

例:

#include <iostream>
#include <fstream>

int main(){
  std::ifstream stream("so.cc");
  stream.exceptions(std::ifstream::failbit|std::ifstream::badbit);
  std::string str;

  try{
    while(std::getline(stream, str));
  }catch(std::ifstream::failure e){
    std::cerr << "Exception happened: " << e.what() << "\n"
      << "Error bits are: "
      << "\nfailbit: " << stream.fail() 
      << "\neofbit: " << stream.eof()
      << "\nbadbit: " << stream.bad() << std::endl;    
  }
  return 0;
}

结果:

Exception happened: basic_ios::clear
Error bits are:
failbit: 1
eofbit: 1
badbit: 0

请注意,这两个 eofbit和failbit设置.

也可以看看:

• std::ios_base::iostate
• §27.5.3.1.5中的表124(见上文)