Programming Forums > Application Development > C++

Ancient Dragon · Jun 1st, 2005, 3:59 PM

How do you delete what's in a stringstream so that is can be used again for something else? I've googled for stringstream and saw a few suggestions, but none of them work. For example

(Toggle Plain Text)

string FormatNumber(string& str)
{
	int n;
	stringstream s(str);
	s >> n;
	s << setfill(' ') << setw(5) << n;
	return s.str();
}

In the above, if " 123.45" is passed to FormatNumber(), the result will be " 123123.45", obviously not what I want. I want the result to be " 123". But how to do this without using a second stringstream object?

Thanks for any suggestions.

jubitzu · Jun 1st, 2005, 5:30 PM

(Toggle Plain Text)

s.str("");

that should do it...

Ancient Dragon · Jun 1st, 2005, 6:33 PM

Thanks a lot. That solved the proglem.

jubitzu · Jun 3rd, 2005, 5:49 AM

I want to recommend a book to you: C++ in a Nutshell ~$40

It has proved invaluable in my programming work and will answer almost any question you could ever conceive about C++ and the STL.

Ancient Dragon · Jun 3rd, 2005, 9:25 AM

This function is not consistent -- when the input string contains a decimal value (such as "123.45" the function works as expected. But if the input string does not contain a decimal (e.g. "123") the result streamstring object is "". Can anyone explain that behavior? I use VC++ 6.0, and used its debugger to step through the code. The value of n is correct in all cases. Its only the final line that is failing.

(Toggle Plain Text)

string FormatNumber(string& str, int width)
// Converts str to an integer (truncating any deaimals that
// it might contain, then reformats the int to (width)-digit string,
// right justified and left-padded with spaces.
//
// For example, the input string str might be " 123.45".  The
// final result of this function will be "  123".  
{
//	static char iobuf[40];
//	sprintf(iobuf,"%*d",width,atoi(str.c_str()));
//	return iobuf;

	int n = 0;
	stringstream s(str);
	s >> n;
	s.str("");
	s << setfill(' ') << setw(width) << n;
#if defined(_DEBUG)
             cout << "s.str() = '" << s.str() << "'";
	if(s.str() == "")
		cout << "\tBAD";
	cout << endl;
#endif
	return s.str();
}

This is really a simple problem in C -- and NEVER fails. Of course the danger here is that a buffer overflow may occur for large values of width. But since I'm in total control of the program, that will never happen. That stringstream class really sucks :mad:

(Toggle Plain Text)

string FormatNumber(string& str, int width)
{
   static char iobuf[20];
   sprintf(iobuf,"%*d",width, atoi(str.c_str());
   return iobuf;
}

mitakeet · Jun 3rd, 2005, 9:31 AM

What are you trying to did anyway? Just convert an int to a string?

Ancient Dragon · Jun 3rd, 2005, 9:36 AM

Quote:

Originally Posted by mitakeet

What are you trying to did anyway? Just convert an int to a string?

remove any decimals that may be in the string and format it to a fixed-width string for output to a lazer printer.

Example:

input strijng: "123.0"
output string to 5 places: " 123"

mitakeet · Jun 3rd, 2005, 9:40 AM

I have never developed a fondness for C++ io, so I would probably do exactly what you are doing in your FormatNumber routine, sorry.

Animatronic · Jun 3rd, 2005, 9:46 AM

The stringstream is failing because you are reaching the end of the stream and then trying to use it again. After you take out an int the stream is empty so the badbit is set and any operations on the stream after that will fail.

You can use setstate() to change the current state of the stream back to good, e.g.:

(Toggle Plain Text)

string FormatNumber(string const & str, int width)
// Converts str to an integer (truncating any deaimals that
// it might contain, then reformats the int to (width)-digit string,
// right justified and left-padded with spaces.
//
// For example, the input string str might be " 123.45".  The
// final result of this function will be "  123".  
{
	//	static char iobuf[40];
	//	sprintf(iobuf,"%*d",width,atoi(str.c_str()));
	//	return iobuf;

	int n = 0;
	stringstream s(str);
	s >> n;
	s.str("");
	s.setstate( stringstream::goodbit );
	s << setfill(' ') << setw(width) << n;
#if defined(_DEBUG)
	cout << "s.str() = '" << s.str() << "'";
	if(s.str() == "")
		cout << "\tBAD";
	cout << endl;
#endif
	return s.str();
}

Ancient Dragon · Jun 3rd, 2005, 9:51 AM

Quote:

Originally Posted by Animatronic

The stringstream is failing because you are reaching the end of the stream and then trying to use it again. After you take out an int the stream is empty so the badbit is set and any operations on the stream after that will fail.

You can use setstate() to change the current state of the stream back to good, e.g.:

Good idea, but it doesn't work either.

Jun 1st, 2005, 3:59 PM	#1
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	stringstream [solved] How do you delete what's in a stringstream so that is can be used again for something else? I've googled for stringstream and saw a few suggestions, but none of them work. For example (Toggle Plain Text) string FormatNumber(string& str) { int n; stringstream s(str); s >> n; s << setfill(' ') << setw(5) << n; return s.str(); } string FormatNumber(string& str) { int n; stringstream s(str); s >> n; s << setfill(' ') << setw(5) << n; return s.str(); } In the above, if " 123.45" is passed to FormatNumber(), the result will be " 123123.45", obviously not what I want. I want the result to be " 123". But how to do this without using a second stringstream object? Thanks for any suggestions. Last edited by Ancient Dragon; Jun 1st, 2005 at 6:36 PM.

Jun 1st, 2005, 5:30 PM	#2
jubitzu Newbie Join Date: May 2005 Location: Colorful Colorado Posts: 25 Rep Power: 0	(Toggle Plain Text) s.str(""); s.str(""); that should do it... __________________ How to ask questions the smart way

Jun 1st, 2005, 6:33 PM	#3
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	stringstream <solved> Thanks a lot. That solved the proglem.

Jun 3rd, 2005, 5:49 AM	#4
jubitzu Newbie Join Date: May 2005 Location: Colorful Colorado Posts: 25 Rep Power: 0	I want to recommend a book to you: C++ in a Nutshell ~$40 It has proved invaluable in my programming work and will answer almost any question you could ever conceive about C++ and the STL. __________________ How to ask questions the smart way

Jun 3rd, 2005, 9:25 AM	#5
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 549 Rep Power: 4	stringstream (not finished afterall) This function is not consistent -- when the input string contains a decimal value (such as "123.45" the function works as expected. But if the input string does not contain a decimal (e.g. "123") the result streamstring object is "". Can anyone explain that behavior? I use VC++ 6.0, and used its debugger to step through the code. The value of n is correct in all cases. Its only the final line that is failing. (Toggle Plain Text) string FormatNumber(string& str, int width) // Converts str to an integer (truncating any deaimals that // it might contain, then reformats the int to (width)-digit string, // right justified and left-padded with spaces. // // For example, the input string str might be " 123.45". The // final result of this function will be " 123". { // static char iobuf[40]; // sprintf(iobuf,"%d",width,atoi(str.c_str())); // return iobuf; int n = 0; stringstream s(str); s >> n; s.str(""); s << setfill(' ') << setw(width) << n; #if defined(_DEBUG) cout << "s.str() = '" << s.str() << "'"; if(s.str() == "") cout << "\tBAD"; cout << endl; #endif return s.str(); } string FormatNumber(string& str, int width) // Converts str to an integer (truncating any deaimals that // it might contain, then reformats the int to (width)-digit string, // right justified and left-padded with spaces. // // For example, the input string str might be " 123.45". The // final result of this function will be " 123". { // static char iobuf[40]; // sprintf(iobuf,"%d",width,atoi(str.c_str())); // return iobuf; int n = 0; stringstream s(str); s >> n; s.str(""); s << setfill(' ') << setw(width) << n; #if defined(_DEBUG) cout << "s.str() = '" << s.str() << "'"; if(s.str() == "") cout << "\tBAD"; cout << endl; #endif return s.str(); } This is really a simple problem in C -- and NEVER fails. Of course the danger here is that a buffer overflow may occur for large values of width. But since I'm in total control of the program, that will never happen. That stringstream class really sucks :mad: (Toggle Plain Text) string FormatNumber(string& str, int width) { static char iobuf[20]; sprintf(iobuf,"%d",width, atoi(str.c_str()); return iobuf; } string FormatNumber(string& str, int width) { static char iobuf[20]; sprintf(iobuf,"%d",width, atoi(str.c_str()); return iobuf; } Last edited by Ancient Dragon; Jun 3rd, 2005 at 9:31 AM.

Jun 3rd, 2005, 9:31 AM	#6
mitakeet Programmer Join Date: Jun 2005 Location: Maryland, USA Posts: 59 Rep Power: 4	What are you trying to did anyway? Just convert an int to a string? __________________ Free code: http://sol-biotech.com/code/. It is not that old programmers are any smarter or code better, it is just that they have made the same stupid mistake so many times that it is second nature to fix it. --Mitakeet The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man. --George Bernard Shaw

Jun 3rd, 2005, 9:40 AM	#8
mitakeet Programmer Join Date: Jun 2005 Location: Maryland, USA Posts: 59 Rep Power: 4	I have never developed a fondness for C++ io, so I would probably do exactly what you are doing in your FormatNumber routine, sorry. __________________ Free code: http://sol-biotech.com/code/. It is not that old programmers are any smarter or code better, it is just that they have made the same stupid mistake so many times that it is second nature to fix it. --Mitakeet The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man. --George Bernard Shaw

Jun 3rd, 2005, 9:46 AM	#9
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	The stringstream is failing because you are reaching the end of the stream and then trying to use it again. After you take out an int the stream is empty so the badbit is set and any operations on the stream after that will fail. You can use setstate() to change the current state of the stream back to good, e.g.: (Toggle Plain Text) string FormatNumber(string const & str, int width) // Converts str to an integer (truncating any deaimals that // it might contain, then reformats the int to (width)-digit string, // right justified and left-padded with spaces. // // For example, the input string str might be " 123.45". The // final result of this function will be " 123". { // static char iobuf[40]; // sprintf(iobuf,"%d",width,atoi(str.c_str())); // return iobuf; int n = 0; stringstream s(str); s >> n; s.str(""); s.setstate( stringstream::goodbit ); s << setfill(' ') << setw(width) << n; #if defined(_DEBUG) cout << "s.str() = '" << s.str() << "'"; if(s.str() == "") cout << "\tBAD"; cout << endl; #endif return s.str(); } string FormatNumber(string const & str, int width) // Converts str to an integer (truncating any deaimals that // it might contain, then reformats the int to (width)-digit string, // right justified and left-padded with spaces. // // For example, the input string str might be " 123.45". The // final result of this function will be " 123". { // static char iobuf[40]; // sprintf(iobuf,"%d",width,atoi(str.c_str())); // return iobuf; int n = 0; stringstream s(str); s >> n; s.str(""); s.setstate( stringstream::goodbit ); s << setfill(' ') << setw(width) << n; #if defined(_DEBUG) cout << "s.str() = '" << s.str() << "'"; if(s.str() == "") cout << "\tBAD"; cout << endl; #endif return s.str(); }

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