Get bytes from a string in C++

This post will discuss how to get bytes from a string in C++.

1. Using `std::transform`

Since C++11, we can use std::byte to represent the actual byte data. We can use the std::transform function to transform a string into a vector of bytes:

#include <iostream>

#include <string>

#include <algorithm>

#include <cstddef>

std::vector<std::byte> getBytes(std::string const &s)

{

std::vector<std::byte> bytes;

bytes.reserve(std::size(s));

std::transform(std::begin(s), std::end(s), std::back_inserter(bytes), [](char const &c){

return std::byte(c);

});

return bytes;

}

int main()

{

std::string s = "Hello, World";

std::vector<std::byte> bytes = getBytes(s);

for (auto byte: bytes) {

std::cout << std::to_integer<int>(byte) << ' ';

}

return 0;

}

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Output:

72 101 108 108 111 44 32 87 111 114 108 100

We can even write custom logic for transforming a string to a vector of bytes using a range-based for loop. Here’s what the code would look like:

#include <iostream>

#include <string>

#include <algorithm>

#include <cstddef>

std::vector<std::byte> getBytes(std::string const &str)

{

std::vector<std::byte> bytes;

for (char const &c: str) {

bytes.push_back(std::byte(c));

}

return bytes;

}

int main()

{

std::string str = "Hello, World";

std::vector<std::byte> bytes = getBytes(str);

for (auto byte: bytes) {

std::cout << std::to_integer<int>(byte) << ' ';

}

return 0;

}

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Output:

72 101 108 108 111 44 32 87 111 114 108 100

2. Using `c_str()` function

A simple solution to get bytes from a string is using the c_str() function that returns read-only const char*.

#include <iostream>

#include <string>

int main()

{

std::string str = "Hello, World";

char const *c = str.c_str();

std::cout << c << std::endl; // Hello, World

return 0;

}

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To get non-const memory having the write access, we can pass the const char* returned by c_str() to the strcpy() function and get a pointer to the char array. To get a char array instead, we can copy the data to bytes using the std::copy standard copy algorithm:

#include <iostream>

#include <string>

#include <algorithm>

int main()

{

std::string str = "Hello, World";

unsigned char bytes[str.length()];

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

std::cout << bytes << std::endl; // Hello, World

return 0;

}

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To convert a string into a vector of bytes, we can use the range constructor of vector:

#include <iostream>

#include <string>

#include <vector>

int main()

{

std::string str = "Hello, World";

std::vector<char> bytes(str.begin(), str.end());

bytes.push_back('\0');

char *c = &bytes[0];

std::cout << c << std::endl; // Hello, World

return 0;

}

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That’s all about getting bytes from a string in C++.

Get bytes from a string in C++

1. Using std::transform

2. Using c_str() function

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1. Using `std::transform`

2. Using `c_str()` function