Question

Update: for the getValue function I have no control, so is there anything I can do from my side?

I have a kind of dumb question about string and char * basic.

I’m using a function that returns a char * value,

const char *getValue(const char *key)
{
    //if key found, and valueString is a string
      return valueString.c_str();
    //else
      return NULL;
}

then I initialized a string to hold the return value,

std::string value = getValue(key);

problem is, whenever the value is not found, which means the function returns NULL, my assignment line will run into an exception. But when there is a legal return value, everything is working fine.

I’m wondering
1. Is this usage totally wrong? means I should never mix char * with string?
2. If not, then when there is a legal pointer returned, does my string automatically make a copy and store it?
3. What is the best way to do this?

Thanks.

Answer 1

Since you have no control over what the getValue() function does, you need to check the return value for NULL before assigning it to the std::string.

std::string value;  // value is an empty string
const char *retVal = NULL;

if( ( retVal = getValue(key) ) != NULL ) {
  value.assign( retVal );
}