Convert string vector to char array in c++

Question

I'm trying to convert a string vector to a char array in c++.

More specifically what I'm trying to do is to split a shell command like "ls –latr" by using this:

istringstream f(x);
while (getline(f, x, ' '))
{
    strings.push_back(x);
}

I believe that will give me strings[0] == "ls" and strings[1]==" -latr".

I'm trying then to do the following:

execvp(strings[0], strings);

however, I get this error:

error: cannot convert ‘std::basic_string, std::allocator >’ to ‘const char*’ for argument ‘1’ to ‘int execvp(const char*, char* const*)’

Therefore, I'm trying to figure out how I can convert the strings to a char array.

add .c_str() to the end of strings[0]; you'll still have to build another vector of pointers for the second parameter though. — Kal
– Kal, Commented Oct 20, 2013 at 20:32
Assuming strings is a std::vector<std::string>, use strings[0].c_str(). the second paramater needs an array of pointers, so that's more complex. — Roddy
– Roddy, Commented Oct 20, 2013 at 20:33
Instead of the getline, you can simply say while (f >> x) { strings.push_back(x); }. — Kerrek SB
– Kerrek SB, Commented Oct 20, 2013 at 21:02

Kerrek SB · Accepted Answer · 2013-10-20 20:45:04Z

7

Reading the manual reveals that "execvp provides an array of pointers to null-terminated strings". So you need to create such an array. Here's one way:

std::vector<char *> argv(strings.size() + 1);    // one extra for the null

for (std::size_t i = 0; i != strings.size(); ++i)
{
    argv[i] = &strings[i][0];
}

execvp(argv[0], argv.data());

edited Oct 20, 2013 at 20:45

answered Oct 20, 2013 at 20:36

Kerrek SB

480k96 gold badges904 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

16 Comments

sehe Over a year ago

Not enough transform :) I've just added a C++03 proof transform answer. Painful stuff

Kerrek SB Over a year ago

@sehe: I can never quite be bothered with transform. I always feel it's a lot of work with no gain.

sehe Over a year ago

@KerrekSB Yeah, Boost Range has transformed, which is a lot more useful indeed. However, before C++11 I think it was frequently a "better for_each"

Kerrek SB Over a year ago

I've changed it from strings[i].front() to strings[i][0] so it is always correct, independent of whether the string is empty.

Roddy Over a year ago

@KerrekSB : I'm fine with std::vector, but I still have problems remembering how char *s get initialized!

|

Igor Popov · Accepted Answer · 2013-10-21 19:48:22Z

1

You may try with c_str() method of std::string. It returns C-like string from the std::string class, i.e. char * which you need for execvpe. Check this link for more details.

edited Oct 21, 2013 at 19:48

user283145

answered Oct 20, 2013 at 20:34

Igor Popov

2,64021 silver badges20 bronze badges

Comments

Vlad from Moscow · Accepted Answer · 2013-10-20 20:34:54Z

0

If the char array will not be changed you can use

strings[0].c_str()

answered Oct 20, 2013 at 20:34

Vlad from Moscow

313k27 gold badges204 silver badges358 bronze badges

Collectives™ on Stack Overflow

Convert string vector to char array in c++

3 Answers 3

16 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

16 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related