convert a char* to std::string
C++StdstringC++ Problem Overview
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?
C++ Solutions
Solution 1 - C++
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.
Solution 2 - C++
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);
Solution 3 - C++
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
Solution 4 - C++
> I need to use std::string to store data retrieved by fgets().
Why using fgets()
when you are programming C++? Why not std::getline()
?
Solution 5 - C++
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();
Solution 6 - C++
const char* charPointer = "Hello, World!\n";
std::string strFromChar;
strFromChar.append(charPointer);
std::cout<<strFromChar<<std::endl;
Solution 7 - C++
char* data;
stringstream myStreamString;
myStreamString << data;
string myString = myStreamString.str();
cout << myString << endl;
Solution 8 - C++
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;
Solution 9 - C++
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 !
Solution 10 - C++
char* data;
std::string myString(data);
Solution 11 - C++
Converting from C style string to C++ std string is easier
There is three ways we can convert from C style string to C++ std string
First one is using constructor,
char chText[20] = "I am a Programmer";
// using constructor
string text(chText);
Second one is using string::assign
method
// char string
char chText[20] = "I am a Programmer";
// c++ string
string text;
// convertion from char string to c++ string
// using assign function
text.assign(chText);
Third one is assignment operator(=), in which string class uses operator overloading
// char string
char chText[20] = "I am a Programmer";
// c++ string
// convertion from char string to c++ string using assignment operator overloading
string text = chText;
third one can be also write like below -
// char string
char chText[20] = "I am a Programmer";
// c++ string
string text;
// convertion from char string to c++ string
text = chText;
Third one is little straight forward and can be used in both situation
- while we are declaring and initializing
- while we are assigning multiple times after object creation or initialization
Solution 12 - C++
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';