How to convert string to char?

Question

I have a problem to output a string. Can you help me?

In the following, const char * i and const char ** o are given.

The statement, "*o = temp" produces an error, saying that "std::string" and "const char *" do not fit. What is the problem?

int mytask(const char * i, const char ** o)
{
    std::string temp = std::string("mytask:") + i;

    *o = temp; //How to modify?

    return (0);
}

Use [`std::copy()`](http://en.cppreference.com/w/cpp/algorithm/copy). — πάντα ῥεῖ, Jun 15 '14 at 06:19
What are you trying to do? Do you want to copy the contents of `temp` in to `*o`? And why are you passing a `char **`? Does `mytask` need to allocate memory for the the string as well? — Praetorian, Jun 15 '14 at 06:25
It would help a lot if you told us what you were trying to do. It looks like you're trying to make `o` point into an object that will no longer exist when you return. — David Schwartz, Jun 15 '14 at 06:38
Why is it `const char **o`? You are trying to modify it in function then why `const`? — , Jun 15 '14 at 06:39

score 1 · Answer 1 · answered Jun 15 '14 at 06:42

1

First of all you are trying to assign a local char pointer and use it in calling function, where it have already been destroyed. So instead you should do this. Assuming memory is allocated for o:

strcpy(*o,temp.c_str());

answered Jun 15 '14 at 06:42

Nisarg

11
2

score 1 · Answer 2 · answered Jun 15 '14 at 06:49

*o=temp means you are making the o point to a pointer that points to a std::string however o is a pointer that points to a char (or sequence of chars). This is not allowed. The other way around works: temp=*o because the std::string object defines what happens when you assign a char* to it (copy the null terminated string into the object). If you absolutely must copy from temp into the char* pointed to by o*. use strcpy() and std::string.c_str() strcpy(*o,temp.c_str())

score 1 · Answer 3 · answered Jun 15 '14 at 06:59

In C++, it's unusual to pass raw pointers around in this manner.

Returning 0 doesn't achieve much either.

I'd expect to see something like this:

std::string mytask(std::string const& i)
{
    return "mytask:" + i;
}

int main()
{
    std::string const number { '1' };
    std::string const ret { mytask(number) };
}

score 0 · Answer 4 · answered Jun 16 '14 at 03:54

0

The statement strcpy(*o,temp.c_str()); didn't work. I resolved this problem by *o = temp.c_srt(); instead. Thanks all anyway.

answered Jun 16 '14 at 03:54

gnoejh

325
4
16

How to convert string to char?

4 Answers4