从文件中提取第一个和最后一个值. [英] Extract first and last values from a file.

问题描述

大家好，
我是一个读取文件并提取值的函数，我该如何仅提取第一个和那个.最后的值.要阅读，我使用此功能:

Hi all,
I a function that reads a file and extract the values, how can I extract only the first and the. last values. To read I use this function:

if (csf.Open(fname, CFile::modeRead)) // CStdioFile csf;
  { 
    while (csf.ReadString(buffer)) //CString buffer;

    {
       int out = 0;
       out = swscanf_s(buffer, _T("%[^,],%[^,],%[^,],%lf"),str1, 2046, str2, 2046, str3, 2046, &db1) );
       // my calculations to process the double values here
    }
      csf.Close();
  }

更新的代码:基于KarstenK的代码:-

Updated code: Based on KarstenK''s code :-

if (csf.Open(fname, CFile::modeRead)) // CStdioFile csf;
  {
    csf.ReadString(buffer);
   //here is first read in the buffer
    int out = 0;
    out = swscanf_s(buffer, _T("%[^,],%[^,],%[^,],%lf"),str1, 2046, str2, 2046, str3, 2046, &db1) );
    pInitialTime = str1;

  while (csf.ReadString(buffer)) {
   //AFTER that is the last readin the buffer
    out = swscanf_s(buffer, _T("%[^,],%[^,],%[^,],%lf"),str1, 2046, str2, 2046, str3, 2046, &db1) );
     pFinalTime = str1; 
 } 
  csf.Close();
  of.WriteString(FmtValues1(pInitialTime, pFinalTime)); // both pInitialTime and pFinalTime values take the last value
    }

我可以使用它读取每一行并进行处理，但是如何只提取第一个和最后一个值呢?

Using this I can read each line and do processing, but how can I extract only the first and the last values?

推荐答案

您只是在Karsten中错过了一个分号'' s代码，while语句末尾的代码.编写这样的while语句也不是一个好习惯.当文件的最后一行为空时，Karsten的代码也没有准备好.

这是一个可以帮助您更好的修订版本:

You just missed one semicolon in Karsten''s code, the one at the end of the while statement. It is also no good practice to code a while statement like this. Also Karsten''s code was not prepared for when the last line of the file is empty.

Here is a revised version that will help you better:

if (csf.Open(fname, CFile::modeRead)) // CStdioFile csf;
  {
    csf.ReadString(buffer);
        //here is first read in the buffer
    int out = 0;
    out = swscanf_s(buffer, _T("%[^,],%[^,],%[^,],%lf"),str1, 2046, str2, 2046, str3, 2046, &db1) );
    pInitialTime = str1;

    // allocate a temp buffer
    CString tempBuffer;

    // now read all remaining lines of the file without decoding them 
    while (csf.ReadString (tempBuffer))
      if (tempBuffer.GetLength() > 0)
          buffer = tempBuffer;

    // now the last non-empty line is in the buffer and we decode it
    out = swscanf_s(buffer, _T("%[^,],%[^,],%[^,],%lf"),str1, 2046, str2, 2046, str3, 2046, &db1) );
     pFinalTime = str1; 
 } 
  csf.Close();
  of.WriteString(FmtValues1(pInitialTime, pFinalTime)); // both pInitialTime and pFinalTime values take the last value
    }

if (csf.Open(fname, CFile::modeRead)) // CStdioFile csf;
  {
    CString buffer;
    csf.ReadString(buffer);
   //here is first read in the buffer

    while (csf.ReadString(buffer));
   //AFTER that is the last readin the buffer

看起来很简单；-)

it looks so easy ;-)

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