Thank you for your apply and It's is C027 board the code is : int MDMParser::sendFormated(const char* format, ...) { char buf[MAX_SIZE]; va_list args; va_start(args, format); int len = vsnprintf(buf,sizeof(buf), format, args); va_end(args); return send(buf, len); }

and i am confused that sendFormated("AT E0\r\n"); why it just a string like printf something ? Is data "AT E0\r\n" or it's just a command ? sending to computer?

From the header file:

   /** Write formated date to the physical interface (printf style)
        \param fmt the format string
        \param .. variable arguments to be formated
        \return bytes written
    */
    int sendFormated(const char* format, ...);

It is exactly like printf only sending the data over the modem. If you are sending a fixed string then it's pointless but if you are sending a variable string then it's useful. e.g.

int echomode = 0;
sendFormated("AT E%d\r\n",echomode);

Thanks but i see the same like you say just like below(MDM.CPP) : sendFormated("AT E0\r\n"); 、sendFormated("AT+CMEE=2\r\n"); 、sendFormated("AT+IPR=115200\r\n"); Are they pointless? Do they need to type like below sendFormated("AT E %d\r\n",0); 、sendFormated("AT+CMEE=%d\r\n",2); 、sendFormated("AT+IPR=%d\r\n",115200); or they are the same?

sendFormated("AT E0\r\n"); and sendFormated("AT E %d\r\n",0); would have exactly the same end result but the second one will be slower since the string has to be formatted.

send("AT E0\r\n", 7) would also have the same effect but would be faster and use less memory since it avoids any calls to the printf string formatting routines.

The big advantage in sendFormated is that the variables don't have to be constant.

This is exactly the same as printf in normal c code.

WOW Thank you very much!! You are a kind person~ I am from Taiwan. My English is poor HAHA. Thank you very much again!!!