Copy string data with NULL character inside string to char array

Question

I am trying to copy one string to char array, string have multiple NULL character. My problem is when first NULL character encountered my program stops copying the string.

I have used two approaches. This is what I am so far.

#include<iostream>
#include<string.h>
using namespace std;

int main()
{
    std::string str = "Hello World.\0 How are you?\0";
    char resp[2000];
    int i = 0;
    memset(resp, 0, sizeof(resp));
    /* Approach 1*/
    while(i < str.length())
    {
            if(str.at(i) == '\0')
            str.replace(str.begin(), str.begin()+i, " ");
        resp[i] = str.at(i);
        i++;
    }
    /* Approach 2*/
    memcpy(resp, str.c_str(), 2000);
    cout << resp << endl;
    return 0;
}

This program should print Hello World. How are you?. Please help me to correct this.

If you print str.length(), is it 12 or 24(ish)? I think your initialization is wrong. You will need to insert the 0 in the middle manually. — Mats Petersson
– Mats Petersson, Commented Apr 7, 2014 at 8:41
I believe cout should output string only to the first zero byte anyway, am I wrong? — Ryzhehvost
– Ryzhehvost, Commented Apr 7, 2014 at 9:06

user657267 · Accepted Answer · 2014-04-22 04:17:59Z

1

You could also one-shot it with

std::transform(
  str.begin(), str.end(), resp, [](char c) { return c == '\0' ? ' ' : c; }
);

Of course as @Mats has mentioned your string doesn't have any null chars, strings can also be initialized as follows though:

char const cstr[] = "Hello World.\0 How are you?";
std::string str(cstr, sizeof cstr);

C++14 has a std::string literal operator

std::string str = "Hello World.\0 How are you?"s;

edited Apr 22, 2014 at 4:17

answered Apr 7, 2014 at 9:22

user657267

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1 Comment

M.M Over a year ago

This includes the trailing null also; possibly sizeof cstr - 1 was intended

juanchopanza · Accepted Answer · 2014-04-07 08:42:26Z

0

Use std::copy:

std::copy(str.begin(), str.end(), std::begin(resp));

followed by std::replace:

std::replace(std::begin(resp), std::begin(resp) + str.size(), '\0', ' ');

You may want to define your character array so that it is full of zeros at the start:

char resp[2000] = {};

answered Apr 7, 2014 at 8:42

juanchopanza

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3 Comments

someone Over a year ago

stringtoarray.cpp:23: error: begin' is not a member of std'

juanchopanza Over a year ago

@someone You must be compiling with a pre-C++11 compiler. You can use &resp[0] instead.

Mats Petersson Over a year ago

Of course, that won't help the fact that the std::string is only initialized with the C-style string up to the first zero. You can have a std::string with NUL-characters in it, but you can't get it from a C-style string (in the way the original code does, at least).

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