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C++ Discussion Thread
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Feb 5th, 2009

Checking if a string is an unsigned integer

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Hi,

I'm having problems checking whether a string is an unsigned integer. The code I am using only checks the first character of the string, so "a1" would return false, but "1a" would return true. Any ideas where I'm going wrong?

C++ Syntax (Toggle Plain Text)
bool checkUnsignedInt(string *str)
{
	unsigned long value;
	stringstream ss(*str);
 
	if (ss >> value)
	{
		return true;
	}
	else
	{
		return false;
	}
}
bool checkUnsignedInt(string *str)
{
	unsigned long value;
	stringstream ss(*str);

	if (ss >> value)
	{
		return true;
	}
	else
	{
		return false;
	}
}

Thanks

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jraven1

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Feb 5th, 2009

Re: Checking if a string is an unsigned integer

What exactly is the problem? this works fine for me....nvm

EDIT:
of you need to loop through each character rather than just using the first one

Chris

Last edited by Freaky_Chris; Feb 5th, 2009 at 1:31 pm.

Freaky_Chris

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Feb 6th, 2009

Re: Checking if a string is an unsigned integer

Maybe something like this comes helpful:

C++ Syntax (Toggle Plain Text)
 
 
bool checkUnsignedInt(string *str)
{
	unsigned long value;
	stringstream ss(*str);
 
	if (ss >> value)
	{
                string str;
                ss >> str;
                return str.empty(); // nothing following the digits
	}
	return false;
}

bool checkUnsignedInt(string *str)
{
	unsigned long value;
	stringstream ss(*str);

	if (ss >> value)
	{
                string str;
                ss >> str;
                return str.empty(); // nothing following the digits
	}
	return false;
}

jencas

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Posting Whiz

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Feb 6th, 2009

Re: Checking if a string is an unsigned integer

*Mumbles something about multiple exit points*

Comatose

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Taboo Programmer

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Feb 7th, 2009

Re: Checking if a string is an unsigned integer

You can do that:

C++ Syntax (Toggle Plain Text)
bool checkUnsignedInt(const string &str)
{
	return atoi(str.c_str()) >= 0;
}
bool checkUnsignedInt(const string &str)
{
	return atoi(str.c_str()) >= 0;
}

Last edited by minas1; Feb 7th, 2009 at 4:56 am.

minas1

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Feb 9th, 2009

Re: Checking if a string is an unsigned integer

I think you can simply check if the first character is a numeral.

Last edited by kbshibukumar; Feb 9th, 2009 at 10:01 am.

kbshibukumar

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Feb 9th, 2009

Re: Checking if a string is an unsigned integer

Click to Expand / Collapse Quote originally posted by kbshibukumar ...

I think you can simply check if the first character is a numeral.

Thats what his code does, but that doesn't mean that "1dfjkghdflgh" is an integer, because it isn't. But by your logic it would be.

Chris

Freaky_Chris

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Feb 9th, 2009

Re: Checking if a string is an unsigned integer

c++ Syntax (Toggle Plain Text)
inline bool isUint(const std::string& s)
{
    return s.find_first_not_of("0123456789") == std::string::npos;
}
inline bool isUint(const std::string& s)
{
    return s.find_first_not_of("0123456789") == std::string::npos;
}

ArkM

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