如何在C ++上附加字符串

Question

when it calls function, the latest string left only ex) first call "abc" second call "def" best result is "abc"\\n"def" , actual result : "def"

visual 6.0 C++

void PrintCSV(CArchive &archiveContent, CStringList &strList, CString szSeparator)
{
    if( strList.IsEmpty() )
        return;

    CString strOneRecord;
    POSITION posTail = strList.GetTailPosition();
    POSITION pos;

    for( pos = strList.GetHeadPosition(); pos != posTail; )
    {
        CString str = strList.GetNext( pos );
        strOneRecord += str;
        strOneRecord += szSeparator;
        strOneRecord += "\t";
    }

    strOneRecord += strList.GetNext(posTail);
    strOneRecord += _T("\r\n"); // windows change a line
    archiveContent.WriteString(strOneRecord);
}

ex) first call "abc" and second call "def"

Expected result is "abc\\r\\ndef"

Actual result : "def"

Answer 1

You are correctly appending one string to another string.

The problem is that you overwrite the old file. You must open the file with CFile::modeNoTruncate and go to the end of the file:

CFile file;
if (file.Open(filename, CFile::modeWrite | CFile::modeCreate | CFile::modeNoTruncate))
{
    file.SeekToEnd();

    CArchive ar(&file, CArchive::store);
    PrintCSV(ar, strList, szSeparator);
}

You can also obtain a handle to CArchive 's CFile and go to end of file:

ar.GetFile()->SeekToEnd();

---

Note that CArchive is commonly used for serialization. If you are not doing serialization then skip CArchive . Use CFile directly, or use CStdioFile as follows:

CStdioFile file;
if(file.Open(filename, 
    CFile::typeBinary | CFile::modeWrite | CFile::modeCreate | CFile::modeNoTruncate))
{
    file.SeekToEnd();
    file.WriteString(str);
    file.Close();
}

(add CFile::typeBinary for CStdioFile if you are handling "\\r\\n" yourself)