convert a char* to std::string

Question

I need to use an std::string to store data retrieved by fgets(). To do this I need to convert the char* return value from fgets() into an std::string to store in an array. How can this be done?

Answer 1

std::string has a constructor for this:

const char *s = "Hello, World!";
std::string str(s);

Note that this construct deep copies the character list at s and s should not be nullptr, or else behavior is undefined.

Answer 2

If you already know size of the char*, use this instead

char* data = ...;
int size = ...;
std::string myString(data, size);

This doesn't use strlen.

EDIT: If string variable already exists, use assign():

std::string myString;
char* data = ...;
int size = ...;
myString.assign(data, size);

Answer 3

Most answers talks about constructing std::string.

If already constructed, just use assignment operator.

std::string oString;
char* pStr;

... // Here allocate and get character string (e.g. using fgets as you mentioned)

oString = pStr; // This is it! It copies contents from pStr to oString

Answer 4

I need to use std::string to store data retrieved by fgets().

Why using fgets() when you are programming C++? Why not std::getline()?

Answer 5

Pass it in through the constructor:

const char* dat = "my string!";
std::string my_string( dat );

You can use the function string.c_str() to go the other way:

std::string my_string("testing!");
const char* dat = my_string.c_str();

Answer 6

const char* charPointer = "Hello, World!\n";
std::string strFromChar;
strFromChar.append(charPointer);
std::cout<<strFromChar<<std::endl;

Answer 7

char* data;
stringstream myStreamString;
myStreamString << data;
string myString = myStreamString.str();
cout << myString << endl;

Answer 8

I would like to mention a new method which uses the user defined literal s. This isn't new, but it will be more common because it was added in the C++14 Standard Library.

Largely superfluous in the general case:

string mystring = "your string here"s;

But it allows you to use auto, also with wide strings:

auto mystring = U"your UTF-32 string here"s;

And here is where it really shines:

string suffix;
cin >> suffix;
string mystring = "mystring"s + suffix;

Answer 9

I've just been struggling with MSVC2005 to use the std::string(char*) constructor just like the top-rated answer. As I see this variant listed as #4 on always-trusted http://en.cppreference.com/w/cpp/string/basic_string/basic_string , I figure even an old compiler offers this.

It has taken me so long to realize that this constructor absolute refuses to match with (unsigned char*) as an argument ! I got these incomprehensible error messages about failure to match with std::string argument type, which was definitely not what I was aiming for. Just casting the argument with std::string((char*)ucharPtr) solved my problem... duh !

Answer 10

char* data;
std::string myString(data);

Answer 11

Not sure why no one besides Erik mentioned this, but according to this page, the assignment operator works just fine. No need to use a constructor, .assign(), or .append().

std::string mystring;
mystring = "This is a test!";   // Assign C string to std:string directly
std::cout << mystring << '\n';