GSM SIM-900A接收英文短信msgindex从哪里获取的

GSM（SIM-900A）接收英文短信问题        
                                        sprintf((char*)p,"AT+CMGR=%s",msgindex);     
                                       
                                        if(sim900a_send_cmd(p,"+CMGR:",200)!=0)   
想从原子哥的程序里改一个收到对英短信就开灯的程序，没有使用LCD屏幕,
sprintf((char*)p,"AT+CMGR=%s",msgindex);  这一句中的msgindex不知道是从哪里获取的，求助，谢谢！     
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/*u8 *p,*p1,*p2;u8 timex=0;u8 msgindex[3];u8 msglen=0;u8 msgmaxnum=0;//¶ìDÅ×î′óìõêyu8 key=0;u8 smsreadsta=0;//êÇ·ñÔú¶ìDÅÏÔê¾×′ì¬p=mymalloc(200);//éêÇë200¸ö×Ö½úμÄÄú′æ//LCD_Clear(WHITE); //POINT_COLOR=RED;//Show_Str_Mid(0,30,"ATK-SIM900A ¶á¶ìDÅ2aêÔ",16,240);     //Show_Str(30,50,200,16,"¶áè¡:     ×üDÅÏ￠:",16,0); //kbd_fn_tbl[0]="¶áè¡";//kbd_fn_tbl[1]="·μ»Ø"; //sim900a_load_keyboard(0,180,(u8**)kbd_tbl1);//ÏÔê¾¼üÅì  while(1){//key=sim900a_get_keynum(0,180);//if(key)/*{  if(smsreadsta){LCD_Fill(30,75,239,179,WHITE);//Çå3yÏÔê¾μĶìDÅÄúèYsmsreadsta=0;}if(key<10||key==11){if(msglen<2){ msgindex[msglen++]=kbd_tbl[key-1][0];u2_printf("AT+CLDTMF=2,"%c"rn",kbd_tbl[key-1][0]); } if(msglen==2){key=(msgindex[0]-'0')*10+msgindex[1]-'0';if(key>msgmaxnum){msgindex[0]=msgmaxnum/10+'0';msgindex[1]=msgmaxnum%10+'0';}} }else{if(key==13)if(msglen)msglen--;//é¾3y  if(key==14&&msglen)//Ö′DD¶á衶ìDÅ{ LCD_Fill(30,75,239,179,WHITE);//Çå3y֮ǰμÄÏÔê¾    sprintf((char*)p,"AT+CMGR=%s",msgindex);if(sim900a_send_cmd(p,"+CMGR:",200)==0)//¶á衶ìDÅ{POINT_COLOR=RED;Show_Str(30,75,200,12,"×′ì¬:",12,0);Show_Str(30+75,75,200,12,"à′×Ô:",12,0);Show_Str(30,90,200,12,"½óêÕê±¼ä:",12,0);Show_Str(30,105,200,12,"ÄúèY:",12,0);POINT_COLOR=BLUE;if(strstr((const char*)(USART2_RX_BUF),"UNREAD")==0)Show_Str(30+30,75,200,12,"òѶá",12,0);else Show_Str(30+30,75,200,12,"Î′¶á",12,0);*/sprintf((char*)p,"AT+CMGR=%s",msgindex);   //Õaàï3öÎêìaif(sim900a_send_cmd(p,"+CMGR:",200)!=0)//¶á衶ìDÅ{//p1=(u8*)sim900a_check_cmd("+CMTI:");p1=(u8*)strstr((const char*)(USART2_RX_BUF),",");p2=(u8*)strstr((const char*)(p1+2),""");p2[0]=0;//¼óèë½áêø·û//sim900a_unigbk_exchange(p1+2,p,0);//½«unicode×Ö·û×a»»ÎagbkÂë //Show_Str(30+75+30,75,200,12,p,12,0);//ÏÔê¾μç»°oÅÂëp1=(u8*)strstr((const char*)(p2+1),"/");p2=(u8*)strstr((const char*)(p1),"+");p2[0]=0;//¼óèë½áêø·û//Show_Str(30+54,90,200,12,p1-2,12,0);//ÏÔê¾½óêÕ걼䠠p1=(u8*)strstr((const char*)(p2+1),"r");//Ñ°Õò»Ø3μ·û  if(p1+2) { LED0=!LED0;}//if(strstr((const char*)(p1+2),"on"))  //sim900a_unigbk_exchange(p1+2,p,0);//½«unicode×Ö·û×a»»ÎagbkÂë//Show_Str(30+30,105,180,75,p,12,0);//ÏÔ꾶ìDÅÄúèY//smsreadsta=1;//±ê¼ÇóDÏÔ꾶ìDÅÄúèY else{LED1=!LED1;}  }*/