How do I convert and validate numeric data to a string object?

[Pep]

I have numeric input which I must convert to strings and validate
whilst doing the conversion. I do not want to mix C functions like
strtol in to my c++ code, so I'm trying to implement a C++ method
using examples found in google but none of them work :(

I have this test program to show my misunderstanding of what is going
on. It also tests a second problem where I am trying to reset a
istringstream but need to call the clear() member after the reset,
which as I misunderstand things is not supposed to be required.

#include <sstream>
#include <iostream>

long testLong;
std::string testString;

std::istringstream iss;

iss.exceptions(std::istringstream::eofbit |
std::istringstream::failbit | std::istringstream::badbit);

iss.str(argv[1]);

try
        // supposedly this will throw exception if conversion is non-
numeric
{
        iss >> testLong;
}
catch(std::istringstream::failure& e)
{
        std::cout << "caught a exception geezer! [" << e.what() << "]" <<
std::endl;
}

if (!iss)
 // supposedly this is the way to check for invalid numeric input
{
        std::cout << "conversion was illegal geezer!" << std::endl;
}

std::cout << std::endl << std::endl << "first string [" << testLong <<
"]" << std::endl;
iss.str("second string");
iss.clear(); // should not have to do this but it does not reset the
string stream without it!!!
iss >> testString;
std::cout << std::endl << std::endl << "second string [" << testString
<< "]" << std::endl;

        return(EXIT_SUCCESS);
}

Here is the output of 3 runs, the first with invalid alpha input, the
second with invalid alpha/numeric input and the third with valid
numeric input.

// test run with invalid alpha input
/test this-is-text
caught a exception geezer! [basic_ios::clear]
conversion was illegal geezer!


first string [0]


second string [second]

// test run with invalid mixed alpha/numeric input
./test 123pep89


first string [123]


second string [second]

// test run with valid numeric input
./test 12389
caught a exception geezer! [basic_ios::clear]


first string [12389]


second string [second]

So it appears that none of the methods used are capable of doing what
I require, even though there are hundreds of entries in google that
state this is the way to do?

What are the "caught a exception geezer! [basic_ios::clear]"
exceptions about?

So how can I do what I want to do, which is simply to convert and
validate a numeric input value to a string value?

TIA,
Pep