将printf数据写入c ++ / cli中的字符串变量

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..

Answer 1

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);

Answer 2

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

Answer 3

您是否看过sprintf在您的平台上如何工作？

Answer 4

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;
    }
  }
}