Easily create string message for exception

Hi,
For a long time I’ve wondered if there is a simplier way to do this, but I’ve never found it. If I have the following code:

Code:

---

void SomeClass::SomeMethod(const char *arg) {
  If (someTestOfTheArgFailed)
      throw std::invalid_argument (“Invalid argument ‘” + arg + “’”);
}

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Now obviously the above code doesn’t work, because I can’t do “Invalid argment ‘” + arg. The alternative would be to do:

Code:

---

If (someTestOfTheArgFailed) {
  std::string s;
  s += " Invalid argument '";
  s += arg;
  s += "'";
  throw std::invalid_argument (s);
}

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This works but has needlessly added extra lines.

It would be cool if I could use some kind of printf syntax, or use operator<<.

Is there some clever trick I can use to do this all on one line still? Perhaps a function or macro I could develop? This is just so I can make my error handling code neater. I don't want to have 4-5 lines for each error message.

Thanks
Andrew

Code:

---

void SomeClass::SomeMethod(const char *arg) {
  If (someTestOfTheArgFailed)
      throw std::invalid_argument (std::string(“Invalid argument ‘”) + arg + “’”);
}

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I think Boost has something similar to printf that you can use. However, I'd just do the above for starters....

The easiest way I've found is to make your own exception class that takes a printf style format string and variadic args. I can't recall offhand though if variadic constructors are part of the standard or a MSVC extension...

Anyway, what I usually use is something like:

Code:

---

#include <stdexcept>
#include <cstdarg>
#include <cstdio>

class MyError
  : public std::runtime_error
{
public:
  static const size_t BUFSIZE = 2048;

  MyError(const char* format, ...)
    : std::runtime_error("")
  {
    va_list args;
    char buffer[BUFSIZE];

    va_start(args, format);
    vsprintf(buffer, format, args);
    va_end(args);

    std::runtime_error::operator =(std::runtime_error(buffer));
  }
};

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