Convert char* to string C++

Question

I know the starting address of the string(e.g., char* buf) and the max length int l; of the string(i.e., total number of characters is less than or equal to l).

What is the simplest way to get the value of the string from the specified memory segment? In other words, how to implement string retrieveString(char* buf, int l);.

EDIT: The memory is reserved for writing and reading string of variable length. In other words, int l;indicates the size of the memory and not the length of the string.

This is really basic C++. I'll recommend [a good introductory C++ book](http://stackoverflow.com/q/388242/46642). — R. Martinho Fernandes, Dec 08 '11 at 22:41
Lest there be any confusion: a `std::string` is *not the same* as a `char[]` string in C++. A `std::string` has a lot of other things to it. — BRPocock, Dec 08 '11 at 22:41
When you say "max length" do you mean the string might be shorter than that? — Mark Ransom, Dec 08 '11 at 22:42
@MarkRansom Yes. The memory is reserved for writing and reading string of variable length — Terry Li, Dec 08 '11 at 22:47
Neither of the 2 existing answers really address that situation. You should edit the question to make it clearer. — Mark Ransom, Dec 08 '11 at 22:51
@BenjaminLindley Up to me how to write the string into the memory. I'm not sure what the typical way is in C++. — Terry Li, Dec 08 '11 at 22:58
possible duplicate of [convert a char\* to std::string](http://stackoverflow.com/questions/1195675/convert-a-char-to-stdstring) — user, Apr 06 '14 at 19:00

score 28 · Accepted Answer · edited Oct 28 '18 at 00:09

28

std::string str(buffer, buffer + length);

Or, if the string already exists:

str.assign(buffer, buffer + length);

Edit: I'm still not completely sure I understand the question. But if it's something like what JoshG is suggesting, that you want up to length characters, or until a null terminator, whichever comes first, then you can use this:

std::string str(buffer, std::find(buffer, buffer + length, '\0'));

edited Oct 28 '18 at 00:09

NonCreature0714

5,744
10
30
52

answered Dec 08 '11 at 22:39

Benjamin Lindley

101,917
9
204
274

3

Clever use of find! I never thought to use the not-found return value for anything! – Mooing Duck Dec 09 '11 at 00:16

score 25 · Answer 2 · answered Dec 09 '11 at 14:54

25

char *charPtr = "test string";
cout << charPtr << endl;

string str = charPtr;
cout << str << endl;

answered Dec 09 '11 at 14:54

Taha

1,086
1
10
20

4

This answer is underrated! – intumwa Nov 02 '21 at 16:20

chill · Answer 3 · 2011-12-09T07:13:33.357

3

Use the string's constructor

basic_string(const charT* s,size_type n, const Allocator& a = Allocator());

EDIT:

OK, then if the C string length is not given explicitly, use the ctor:

basic_string(const charT* s, const Allocator& a = Allocator());

edited Dec 09 '11 at 07:13

answered Dec 08 '11 at 22:39

chill

16,470
2
40
44

score 2 · Answer 4 · answered Dec 08 '11 at 23:25

There seems to be a few details left out of your explanation, but I will do my best...

If these are NUL-terminated strings or the memory is pre-zeroed, you can just iterate down the length of the memory segment until you hit a NUL (0) character or the maximum length (whichever comes first). Use the string constructor, passing the buffer and the size determined in the previous step.

string retrieveString( char* buf, int max ) {

    size_t len = 0;
    while( (len < max) && (buf[ len ] != '\0') ) {
        len++;
    }

    return string( buf, len );

}

If the above is not the case, I'm not sure how you determine where a string ends.

If the given string is guaranteed to have a NULL, all you need is `string(buf)` and you're good. If it might not, then you have to use this method. — Mooing Duck, Dec 08 '11 at 23:28

score 1 · Answer 5 · answered Feb 15 '18 at 05:46

1

std::string str;
char* const s = "test";

str.assign(s);

string& assign (const char* s); => signature FYR

Reference/s here.

answered Feb 15 '18 at 05:46

parasrish

3,864
26
32

score 0 · Answer 6 · answered Jun 17 '21 at 07:19

Let,

char* rw="hii";  //This string is readable and writeable

const char* r="hello"; // This string is only readable

we can convert char* or const char* to string with the help of string's constructor.

string string_name(parameter);

This parameter accepts both char* and const char* types .

Examples:

1) string st(rw); 

 Now string 'st', contains "hii"

2) string st(r);

 Now, string 'st' contains "hello".

In both the examples, string 'st' is writable and readable.

Convert char* to string C++

6 Answers6

Linked