对于std :: string :: c_str，无法从'const char *'转换为'char *'

Question

This gives the error: cannot convert from 'const char *' to 'char *'.

class Mock
{
public:
    ...
    static void func(char **result)
    {
          *result = (resultsI++)->c_str();
    }
static std::vector<std::string> results;
static std::vector<std::string>::iterator resultsI;
};

std::vector<std::string> Mock::results;
std::vector<std::string>::iterator Mock::resultsI;

How can I validly get rid of this error without changing the interface to the function func? The implementer of this interface:

void (func*)(char **result) 

forgot to use const char** in the signature. I can't change it.

Remember this is a mock and I'm only used in my unit tests.

Answer 1

Try:

*result = &(*resultsI++)[0];

Although this isn't guaranteed to work prior to C++11 it is known to be OK on most or all current compilers.

The danger is that if the function tries to change the length of the string, you could get some nasty errors. Changing individual characters should be OK.

Answer 2

In test code, and if you are certain that the user of the interface isn't going to mutate the char*, maybe you could use a const_cast ?

That assumes the caller doesn't take ownership of the char * ; if that is the case, then you should make a copy.

Answer 3

If you're absolutely certain that the interface function will not modify the string, you can use

*result = const_cast<char *>((resultsI++)->c_str());

to remove const ness.

Otherwise, another option is to switch from using std::vector<std::string> to std::vector<std::vector<char>> but then you'll have to make sure you properly null terminate the strings.