Trouble using a string with the sprintf() function

Question

I'm hoping that this will be a pretty basic problem that is maybe due to my lack of understanding a lot of the C++ Win32 API utlities.

Anyway, I'm having some trouble with the sprintf() function. I had no problem using it with a string like this:

//memory is a void pointer that maps a file to shared memory sprintf((char *)memory, "Shared memory message"); //Write to shared memory

But when I try to use a string variable it doesn't work....

sprintf((char *)memory, str_var); //Write to shared memory

I get an error that says: no suitable conversion function from "std::string" to "const char *" exists. I am not even able to fix this by type casting, like I did with memory.

This seems pretty inconsistent. What am I doing wrong, and how do I give it a value that it will accept?

std::string cannot be converted to const char*, use the .c_str() member method to convert it — David Szalai
– David Szalai, Commented Nov 28, 2014 at 20:22
try to learn difference between string and c-style string. [stackoverflow.com/questions/10958437/… [1]: stackoverflow.com/questions/10958437/… — BufBills
– BufBills, Commented Nov 28, 2014 at 20:32

sehe · Accepted Answer · 2014-11-28 20:22:15Z

Iff you need sprintf, you need to pass a const char*:

http://linux.die.net/man/3/sprintf

So e.g.

sprintf((char *)memory, str_var.c_str());

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