（c ++）数组元素成字符串？

Question

Can somebody help me in converting some elements of char array[] into String . I'm still learning strings.

char input[40] = "save filename.txt";
int j;
string check;
for (int i = 0; input[i] != '\0'; i++)
{
   if (input[i] == ' ')
   {
      j = i+1;
      break;
   }
}
int index;
for (int m = 0; arr[j] != '\0'; m++)
{
    check[m] = arr[j];
    j++;
    index = m; //to store '\0' in string ??
}
check[index] = '\0';
cout << check; //now, String should output 'filename.txt" only 

Answer 1

The string class has a constructor that takes a NULL-terminated C-string:

char arr[ ] = "filename.txt";

string str(arr);


//  You can also assign directly to a string.

str = "filename.txt";

Answer 2

The ctor of std::string has some useful overloads for constructing a string from a char array. The overloads are about equivalent to the following when used in practice:

• Taking a pointer to constant char , ie a null-terminated C-string.

   string(const char* s); 

  The char array must be terminated with the null character, eg {'t', 'e', 's', 't', '\\0'} . String literals in C++ is always automatically null-terminated, eg "abc" returns a const char[4] with elements {'a', 'b', 'c', '\\0'} .

• Taking a pointer to constant char and specified number of characters to copy.

   string(const char* s, size_type count); 

  Same as above but only count number of characters will be copied from the char array argument. The passed char array does not necessarily have to be null-terminated.

• Taking 2 iterators.

   string(InputIt first, InputIt last); 

  Can be used to construct a string from a range of characters, eg

   const char[] c = "character array"; std::string s{std::next(std::begin(c), 10), std::end(c)}; // s == "array".