Question

Below is the insert function in VC++.
I am getting this error when I change the char to string data type to read the value of amount variable in the below code.

static void Insert(t_analysis* analysis)    
{    
 _bstr_t strunitId;    
 _bstr_t strGdt=time(0);    
_bstr_t strvalue;   
    std::string str;
std::string commandStr = "insert into table1(unitid,g_time_dte_1,h_1,n_1,ch_1,co_1,im_1,ve_1,er_1) Values(123,'" + strGdt +"',";
    char tempBuf[50];
for (int j = 0; j < analysis->ubPeaksIntTab;j++ )
{   
    sprintf(tempBuf, "%d", (analysis->peak + j)->amount);//here it takes the adrress of amount but not the value of amount variable.
    str += commandStr + tempBuf;
    if(j!=analysis->ubPeaksIntTab-1)
       commandStr += ",";
}

commandStr += ")";
_ConnectionPtr pConn = NULL;

try
{       
    HRESULT hr = S_OK;
    CoInitialize(NULL);
    hr = pConn.CreateInstance((__uuidof(Connection)));
    _bstr_t strCon("Provider=SQLOLEDB;Dataq Source=MYPC\\SQLEXPRESS;Initial Catalog=keerth;User ID=sa;Password=password;Connect Timeout=30;");

    if(FAILED(hr))
    {
        printf("Error instantiating Connection object\n");

    }

    hr = pConn->Open(strCon,"sa","password",0);

    if(FAILED(hr))
    {
        printf("Error Opening Database object using ADO _ConnectionPtr \n");

    }

    //Execute the insert statement
    pConn->Execute(commandStr.c_str(), NULL,adExecuteNoRecords);
    pConn->Close();
}
catch(_com_error &ce)
{
    printf("Error:%s\n",ce.ErrorMessage());
    pConn->Close();
}
}

Whenever I run this getting the Error. Then I changed the char tempbuf[50]; to std::string str1;.
Now it is showing:

Error C2664: 'sprintf' : cannot convert parameter 1 from 'std::string' to 'char *;

The amount variable contains the float value.
How can I copy the float value assign it to string variable?

Answer 1

You are mixing C++ with C standard library functions.

You should use the C++ primitives. See StringStreams

#include <iostream>
#include <string>
#include <sstream>

int main () {
  std::stringstream ss;
  ss << "hello world";
  ss << 45;
  ss << std::endl;
  std::string foo = ss.str();
  std::cout << foo;
  return 0;
}

EDIT:

If you want the same logic in C: The type std::string is not a C type, the standard string type of C is char * and const char * for immutable strings.

The functions that you want to look at are then: strncat (concatenate strings) and the safer snprintf.