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I am trying to retrieve values from within a list of strings
SentenceList.h
----------------------------------
#pragma once
..
#include <list>
...
using std::list;
...
class CSentenceList
{
....
string display(unsigned int iLineNumber = 1);
list<string> Sentences; //list of sentences
// Note: MOVE TO PRIVATE AFTER IMPLEMENTING display
....
};
The list is being created and I would like to create a method 'display' that returns a string according to the line number. The method should loop through the list and return a string according to the value of iLineNumber.
I have tried using Sentences.front, but I could not picture the correct return value to be read to return the string value.
How do I read values from Sentences?
Jon
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there you have create an instance of string with size 1. That is the equivlent of char str[1]; So where are the strings that you want to return? For the list object, just treat it like an array. If you want the 10th string just call Sentences[10].
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When I tried the following, the compiler didn't like it...
string CSentenceList::display(unsigned int iLineNumber)
{
return Sentences[iLineNumber];
}
Error:
(51): error C2676: binary '[' : 'std::list<_Ty>' does not define this operator or a conversion to a type acceptable to the predefined operator
with
[
_Ty=std::string
]
Jon
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Oh, sorry my fault, I was confusing list with vector. You are using list, but want to provide a line number. You do realise a list is sorted. Everything you add to it will be rearranged. If you want to add sentences one ata time and keep them in order you should really use the vector class. If you really want to use the list then you will have to go through a loop testing the value of each sentence, but there is no way for you to know which line goes with which sentence.
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You need to use an iterator to traverse the elements in the list.
Try something like:
list<string>::iterator start = Sentences.begin()
while ( start != Sentences.end() )
{
if(sentence matches) // probably want to try something like string == (*start)
{
//do something
break; // if you hit a match break
}
start++;
}
Hope that helps. There are plenty of articles on using iterators as well.
-- modified at 23:54 Sunday 27th August, 2006
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Can we get the info about which operating system is currently present in the system for example is it windows98 or xp or win2000.
Thank you
KIRAN PINJARLA
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To find out the operating system version, use GetVersionEx. Windows 98 is major version 4, minor version 10. Windows 2000 is major 5, minor 0 and Windows XP major 5, minor 1. Windows Server 2003 is major 5, minor 2 and Windows Vista will be major 6, minor 0. Windows XP x64 may return major 5, minor 2 since it is based on the Windows Server 2003 SP1 kernel.
Be careful when testing version numbers. In the past people have frequently got it wrong, causing compatibility problems when new operating systems come out. If targetting Windows 2000 and higher only, it is recommended to use the VerifyVersionInfo API to check the OS version is what you require.
Generally it's recommended not to check the OS version at all, but for any advanced, optional features using functions added in later operating systems, to check whether the function is available using LoadLibrary and GetProcAddress. This covers any cases where the API may be back-ported to an older OS.
If you're trying to test the OS version to determine whether to install, and you're using Windows Installer, you should use a Launch Condition to test the Version9X and/or VersionNT properties. Version9X is only defined on Windows 95, 98 or ME: its value is 400 on Windows 95, 410 on Windows 98 and 490 on Windows ME. VersionNT is defined on NT 4.0, Windows 2000, Windows XP, Windows Server 2003 and later, and has the values, respectively: 400, 500, 501, 502, and 600 for Windows Vista.
At this stage I would consider dropping support for Windows 98. Recent statistics gathered from processing web server logs (e.g. OneStat[^]) suggest that Windows 98 is now used by less than 3% of users of those web sites, with Windows ME used by only a little over 1%. I would expect these numbers to continue to fall.
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The following code should read a text file and update Sentences (defined as std::list<string> Sentences).
However, fstream does not seem to like 'string' types. Is it possible to retain string types and convert it to char?
bool CSentenceList::readFile(const string strFileToRead)
{
string strLine;
fstream fileToRead((char*) strFileToRead,ios::in);
if (ios::good != false)
{while (!fileToRead.eof() && Size < MAX_LINES)
// Read line of text from file and update Sentences.strSentence.
{ fileToRead.getline(strLine, MAX_SENTENCE_LENGTH);
Sentences.push_back(strLine);
Size++;
}
return true;
}
else
{ throw "File cannot be read!";
return false;
}
fileToRead.close();
}
Errors:
SentenceList.cpp(23): error C2440: 'type cast' : cannot convert from 'const std::string' to 'char *'
SentenceList.cpp(28): error C2664: 'std::basic_istream<_Elem,_Traits>::_Myt &std::basic_istream<_Elem,_Traits>::getline(_Elem *,std::streamsize)' : cannot convert parameter 1 from 'std::string' to 'char *'
with
[
_Elem=char,
_Traits=std::char_traits<char>
]
Are there other objects I can use so I can read text files from 'string' types, since they are less prehistoric?
Jon
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First, about std::string, if you want a char*, you should use the c_str() function,
other methods are not safe.
But this is not relevant to your problem. You should take a look at streams.
You'd create an istream, from your file, and then do things like
istream >> strline;
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A precision to my former post.
the istream I was refering to was a stringstream, as you mentionned you were looking
for less prehistoric methods, I think streams provide nice high level objects, but you'd
need to do some readings on the topic.
For a quick fix to your code, you could do something like:
string strLine(MAX_SENTENCE_LENGTH, ' ');
This creates a string with the right size. To read directly into the string buffer,
you can acces it with &(*(strLine.begin())), this gives you a pointer to the internal
buffer.
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OK, where do we start? The constructor for the fstream class does not take a string class, it needs a const char*, easy to fix, call the c_str() member of strFileToRead. That should get your file open. Next you are tring to read the line directly into a string class, this is not possible with the istream class. You must allocate a buffer of type char and read into that, then assign that buffer to the string class.
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(Hope this is not seen as off-topic ! Apologies, if so !) Can anyone point me to an article which describes the generic actions that take place when the drivers for a hardware device get installed in a Windows system ? Is there any API which supports any of these actions ? Thanks !
Doug
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First, you can start with information in the Windows Driver Kit[^]. You'll also need information on the Setup API[^], which handles the INF files used to install drivers.
Unfortunately, the device driver group within Microsoft is a bit of their own private kingdom. Their development tools and documentation aren't nearly up to the standards of the rest of the company. The best approach to handling device driver installation is to adapt their examples until you have something that installs your driver.
Software Zen: delete this;
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Thanks Gary - very useful pointers ! (didn't know about the Setup API which will help enormously - I hope !!)
Doug
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And here we go with another problem. I am declaring a constant string within my code, wrapping it with the _T() macro. In a unicode build this translates to the L prefix. The problem I am having is, my string is actually a multibyte pathname, there are Chinese characters within the string. I am trying to use this string within a function but having problems. With an MBCS build, the string length is 60, but in UNICODE the length is 64. Any ideas?
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In MBCS strings each Chinese character takes two chars, but in wide char strings, each Chinese character only takes one wide char. That will cause the difference in string length.
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In MBCS a Chinese character takes 2 bytes, in UNICODE it also takes 2 bytes. My question is, why does the 'L' macro not map the string correctly. Instead of leaving the Chinese caracters as they are it is breaking them up further, giving each character 4 bytes. How can I overcome this without passing the string through a MultiByteToWideChar() function? I'm sure this does not only apply to Chinese characters, it must be the same with any unicode character enetered into a litteral string.
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I think you cannot escape the call to MultiByteToWideChar. Actually even two, one
for getting the buffer size, and one for filling the buffer.
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Yeah, I figured. I decided to use the ATL macros. But look at this snippet, I can't work it out.
USES_CONVERSION;
length *= 2;
char *text = new char [length+1];
memset(text,0,length+1);
WideCharToMultiByte(936,0,(unsigned short *)data,length/2,text,length+1,NULL,NULL);
strings[_added_strings] = new String( A2T(text) );
_added_strings++;
delete[] text;
data += length;
Basically, I am reading from a byte array which contains UTF16 text. Here I am converting it to multibyte, but for a unicode build I want to leave it as it is. Problem is, if I turn that text into a wchar_t and memcpy the bytes over, I get no text. The only way I can do it is to first convert to multibyte, then convert it back to wide.
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IMO, the difference in length should be related to the string representation.
I would guess the unicode string starts with the length of the string. So
with a simple memcpy you might incorrectly copy the string.
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L"" is not a macro, it's simply a means of indicating a unicode string literal. ie. whatever is within it has to be a valid unicode string. If you're specifying a MBCS string literal then it's within your unicode build that you have to do the conversion from MBCS (specifying the codepage the string is in) to unicode.
You should also consider what happens if for the MBCS build, the user is not running with the codepage that the MBCS string is in. (MBCS strings are all codepage specific). So what happens then? Converting your MBCS string to unicode and then back to the user's current codepage would probably fail (being unable to do the mappings), and using that MBCS string ignoring the user's current codepage is very wrong and might represent invalid file path characters on that user's codepage.
If you are using VC7 and up, you should use the new ATL conversion classes[^]instead though there are some differences.
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The behaviour will depend on the codepage that the compiler uses to read the source file, which is the user's default codepage - for a Western developer, that will normally be Windows-1252. Newer versions of the compilers I think can recognise the Byte Order Mark to handle UTF-16 or UTF-8 source code files (the BOM is the character U+FEFF, so if the file begins with the bytes 0xFF 0xFE, it's likely to be a UTF-16 little-endian file, while if it starts 0xEF 0xBB 0xBF, it's probably a UTF-8 file).
In VS2003 and 2005, you can go to File, Advanced Save Options and specify the encoding to use for a given source file.
You may get best results using either a UTF-8 or UTF-16 source file, if your environment supports it, or using the hex escapes to explicitly specify the characters. I'm not sure if Visual C++ supports the '\u' syntax for specifying Unicode characters directly - I don't think it does.
Note that any Latin characters in your MBCS string will be encoded using one byte, not two: indeed, any character coloured white on, for example, this reference chart[^] (Simplified Chinese CP936).
Finally, you're not explicitly encoding the translation of 'Program Files', are you? There are many locations that you can, and should, discover the localized path for using the SHGetSpecialFolderPath API.
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The file I am reading is a standard Biff8 excel file, going by the docs for the file format I am reading it the correct way. As it happens I don't need to worry to much about dealing with multibyte characters, I live and work in China so I am surrounded by them on a daily basis. My problem is with unicode, utf-7 utf-8 utf-16, little endian, big endian, where does it end?
Usually all my builds are MBCS to be compatible with win95 systems (don't ask), but lately I have begun to realise the importance of unicode. So it looks like I am going to have to start learning all over again.
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#ifdef UNICODE
LPCWSTR str = L"\x4f60\x597d";
#else
LPCSTR str = "\x81\xf1\x8f\x11";
#endif You can't do it with one literal because the contents of the literal have to match the character set that you're compiling for.
--Mike--
Visual C++ MVP 
LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ
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