string with embedded null characters

Question

Is there any way that I can use istringstream to read strings with embedded null characters? For example, if I have a char array "125 320 512 750 333\0 xyz". Is there any way that I could get "xyz" after the null character?

#include <iostream>
#include <sstream>

using namespace std;

int main() {
    std::string stringvalues = "125 320 512 750 333\0 xyz";

    cout << "val: " << stringvalues << endl;

    std::istringstream iss (stringvalues);

    for (int n=0; n<10; n++)
    {
        string val;
        iss >> val;
        std::cout << val << '\n';
    }
    
    return 0;
}

This is an example modified from cplusplus.com. I want to get the part after the null character, and I am curious whether I can get it without knowing the exact length of the char array. Thanks in advance.

Please show some code. `Is there any way that` yes, just use it. — KamilCuk, Nov 22 '20 at 13:01
Please do not post images of text. Please post text as text into your question. — KamilCuk, Nov 22 '20 at 13:04
Use one of the constructors that also takes a length argument. — Shawn, Nov 22 '20 at 13:05
All questions here should have all relevant information ***in the question itself as plain text***. Links can stop working at any time making questions meaningless. Code, data, or errors shown as images cannot be copy/pasted; or edited or compiled for further research and investigation. Please [edit] this question, removing and replacing all links and images with all relevant information as plain text. All code must meet all requirements of a [mre]. You can find many other questions here that explain everything in plain text, please use them as an example for how your question should look. — Sam Varshavchik, Nov 22 '20 at 13:07
Starting at the first character of the array, step through to find the first null character. Then do one more step. Of course, the problem with this is that you must somehow ensure the array has characters in it after the null character, otherwise the behaviour is undefined. — Peter, Nov 22 '20 at 13:15

KamilCuk · Accepted Answer · 2020-11-22T13:13:55.150

Just properly initialize string with the proper size of the char array. The rest will follow naturally.

#include <sstream>
#include <string>
#include <cstring>
#include <iostream>
#include <iomanip>
int main() {
    const char array[] = "125 320 512 750 333\0 xyz";

    // to get the string after the null, just add strlen
    const char *after_the_null_character = array + strlen(array) + 1;
    std::cout << "after_the_null_character:" << after_the_null_character << std::endl;

    // initialized with array and proper, actual size of the array
    std::string str{array, sizeof(array) - 1};
    std::istringstream ss{str};
    std::string word;
    while (ss >> word) {
        std::cout << "size:" << word.size() << ": " << word.c_str() << " hex:";
        for (auto&& i : word) {
            std::cout << std::hex << std::setw(2) << std::setfill('0') << (unsigned)i;
        }
        std::cout << "\n";
    }
}

would output:

after_the_null_character: xyz
size:3: 125 hex:313235
size:3: 320 hex:333230
size:3: 512 hex:353132
size:3: 750 hex:373530
size:4: 333 hex:33333300
size:3: xyz hex:78797a

Note the zero byte after reading 333.

Thanks for answering. Could you explain what do those hex value represent? — Jim Yang, Nov 22 '20 at 13:19
Hex values represent the value of characters stored in `word`. Read about ASCII — KamilCuk, Nov 22 '20 at 13:21

eerorika · Answer 2 · 2020-11-22T13:21:19.023

Is there any way that I can use istringstream to read strings with embedded null characters?

Yes. You can use any of the UnformattedInputFunctions such as the read member function to read input including null chars.

Note however that your stringvalues does not contain anything after the null char and thus neither does the string stream constructed from it. If you want a std::string that contains null chars (other than the terminating one), then you can use for example the constructor that accepts a size as second argument.

I want to get the part after the null character, and I am curious whether I can get it without knowing the exact length of the char array.

Here is a simple way:

const char* string = "125 320 512 750 333\0 xyz";
std::size_t length = std::strlen(string);
const char* xyz = string + length + 1;

string with embedded null characters

2 Answers2