Question

The below line works. It prints Success.

wchar_t * s1 = (wchar_t *) L"INSERT INTO OE(sqltext) VALUES('this text')";

if(WriteToSQL(s1) == 0)
  printf( "Success");     //Success
else
  printf( "Failed");     

I need to take user input to create dynamic sql. I need to do what
L prefix is doing.

When i take input and do the required conversion, it does not work.

char input[100]; 
char sql[500];  

printf("Enter input string :: "); 
fgets(input,100,stdin); 
for(int i=0;i<100;i++) 
    if(input[i]==10) 
        input[i]=0; 

strcpy(sql,"INSERT INTO OE(sqltext) VALUES('"); 
strcat(sql,input); 
strcat(sql,"')"); 

wchar_t wsql[500];  
MultiByteToWideChar( CP_UTF8, 0, sql, strlen(sql), 
wsql, strlen(sql) + 1 );  


if(WriteToSQL(wsql) == 0)
  printf( "Success");     
else
  printf( "Failed");     // It failed

---

Long conversassion but finally it did work. Hex memory dump and input from usta was most helpful. Thanks everybody for their time.

Answer 1

You can’t just cast a char * to wchar_t * and expect it to work. You must do proper conversion, for example using MultiByteToWideChar function.

And in general, be very careful with type casts, and in particular avoid using C-style casts in C++ programs. This very case is a good example of why: you told the compiler to shut up ((SQLWCHAR *) sql), and in return got a problem at runtime. Use casts only when you are absolutely sure you are doing the right thing, and know better than the compiler. Not surprisingly, such cases are relatively rare…