string.c_str() is const? [duplicate]

Question

I have a function in a library that takes in a char* and modifies the data.

I tried to give it the c_str() but c++ docs say it returns a const char*.

What can I do other than newing a char array and copying it into that?

Answer 1

You can use &str[0] or &*str.begin() as long as:

• you preallocate explicitly all the space needed for the function with resize();
• the function does not try to exceed the preallocated buffer size (you should pass str.size() as the argument for the buffer size);
• when the function returns, you explicitly trim the string at the first \0 character you find, otherwise str.size() will return the "preallocated size" instead of the "logical" string size.

Notice: this is guaranteed to work in C++11 (where strings are guaranteed to be contiguous), but not in previous revisions of the standard; still, no implementation of the standard library that I know of ever did implement std::basic_string with noncontiguous storage.

Still, if you want to go safe, use std::vector<char> (guaranteed to be contiguous since C++03); initialize with whatever you want (you can copy its data from a string using the constructor that takes two iterators, adding a null character in the end), resize it as you would do with std::string and copy it back to a string stopping at the first \0 character.