CODEWITHSUNDEEP
c++stringchar
Terry Li
Terry Li

Reputation: 17268

How can you construct a std::string from a char* and a maximum length?

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.

Upvotes: 38

Views: 150466

Answers (6)

Vineeth Peddi
Vineeth Peddi

Reputation: 544

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.

Upvotes: 0

Benjamin Lindley
Benjamin Lindley

Reputation: 103703

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'));

Upvotes: 29

parasrish
parasrish

Reputation: 4152

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

str.assign(s);

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

Reference/s here.

Upvotes: 1

Taha
Taha

Reputation: 1106

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

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

Upvotes: 25

chill
chill

Reputation: 16888

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());

Upvotes: 3

Amish Programmer
Amish Programmer

Reputation: 2121

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.

Upvotes: 2

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