writing printf data to a string variable in c++/cli

Question

I need to send a fomatted data to a tcp ip port in my c++/cli program.I have this code with no success

String^ data;
sprintf(data,"L,%02u%02u%02u%02u%02u%02u%03u,%lf %lf\n",rDateTime.uiYear, rDateTime.usiMonth, rDateTime.usiDay,
                rDateTime.usiHour, rDateTime.usiMinute, rDateTime.usiSec, 
                rDateTime.udiUSec / 1000,container[i].first,container[i].second);

I get the error *error C2664: 'sprintf' : cannot convert parameter 1 from 'System::String ^' to char **

I want to write it to a string variable std::string.

Can someone provide with some suggestions.If atleast I convert it to System::String^. I can convert it to the std:string using this C++/CLI Converting from System::String^ to std::string. But I dont know how to write the different datatypes to a string^ in c++/cli..

`sprintf` would probably be what you're looking for if it's there in cli. — chris, Jul 04 '12 at 03:45
@chris.. I tried that before and i edited my question accordingly — ShivShambo, Jul 04 '12 at 03:54
sprintf() is a native C library function, it requires a char[] as the first argument. A System::String is not a char[]. Either use a char[] and convert to String or use String::Format(). You ought to get up to speed on composite string formatting if you plan to write more C++/CLI code. — Hans Passant, Jul 04 '12 at 03:59
@HansPassant Can I give some sample example code. I am just beginning my steps in c++/cli. — ShivShambo, Jul 04 '12 at 04:52

score 3 · Accepted Answer · answered Jul 04 '12 at 06:31

You need to declare a temperory variable with type char*. I am using a fixed array here for demonstration purpose. Since you may have a long string, I suggest you to look at _snprintf to avoid buffer overflow error.

After you get your string in char*, you can create a managed System::String using gcnew

char str[1024];

sprintf(str,"L,%02u%02u%02u%02u%02u%02u%03u,%lf %lf\n",rDateTime.uiYear, rDateTime.usiMonth, rDateTime.usiDay, 
            rDateTime.usiHour, rDateTime.usiMinute, rDateTime.usiSec,  
            rDateTime.udiUSec / 1000,container[i].first,container[i].second); 

System::String^ data = gcnew System::String(str); 
Console::WriteLine(data);

score 1 · Answer 2 · answered Jul 04 '12 at 06:23

The sprintf() function takes a char array (char *) as it's first argument. If you want to use it in this way, you need to first write into a char array, and then convert it into a string. I don't know about System::String^, but you can convert a char array into an std::string by a simple assigning like this:

char * data = new char[50];
sprintf(data, "Your text goes here");
std::string str = data;

Don't forget to allocate memory for the char array! if you forget it and write something like this:

char * data;
sprintf(data, "Your text goes here");

you are going to get an error. On the other hand, if std::string is suitable for you, you can format it directly using formatting manipulators

Mark Lakata · Answer 3 · 2013-05-09T15:50:43.597

I realize that this is Not The Way To Do It if you are writing new managed code, but if you are porting unmanaged legacy C++ code that works with printf and const char*, there is no reason to rewrite the whole thing Just To Be Right.

This works for me and should safely work for any size string. I use it to wrap some functions that call Trace(...) to give flexibility of having a delegated Action deal with logging messages.

void TraceBase1(const char* prefix, const char* format, va_list argp) {
  if (Logger::m_logDelegate != nullptr) {

    System::String^ message;

    int count = _vscprintf(format,argp) + 1;
    char* buffer = new char[count ];
    try {
        _vsnprintf(buffer,count,format,argp);
        message =  gcnew System::String(buffer);
        Logger::m_logDelegate(message);
    }
    finally {
        delete[] buffer;
    }
  }
}

score 0 · Answer 4 · answered Jul 04 '12 at 03:46

0

Have you looked at how sprintf works on your platform?

answered Jul 04 '12 at 03:46

K. Brafford

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writing printf data to a string variable in c++/cli

4 Answers4