C++ String in Binärdatei speichern

#include <fstream>
#include <iostream>

using std::ofstream;
using std::ifstream;

int main(void)
{
 int num = 439041101;
 ofstream out { "./test.bin", ofstream::binary };
 
 size_t len = sizeof (int);
 size_t idx;
 
 std::cout << std::hex;
 
 for (idx = 0; idx < len; ++idx) {
 const char byte = num >> (idx * 8);
 std::cout << "schreibe byte " << (int)byte << std::endl;
 out.write(&byte, 1);
 }
 
 out.close();
 
 std::cout << std::dec;
 std::cout << "zahl geschrieben: " << num << std::endl;
 
 // ------------------------
 
 ifstream in { "./test.bin", ifstream::binary };
 
 char bin[len];
 in.read(bin, len); // 4 bytes einlesen (sizeof (int))
 in.close();
 
 int res = 0;
 
 std::cout << std::hex;
 
 // unten nach oben verarbeiten, da little-endian
 for (idx = len; idx > 0; --idx) {
 std::cout << "verarbeite byte " << (int)bin[idx - 1] << std::endl;
 res <<= 8;
 res |= bin[idx - 1];
 }
 
 std::cout << std::dec;
 std::cout << "zahl gelesen: " << res << std::endl;
 
 return 0;
}

#include <stddef.h>
#include <stdint.h>
#include <stdio.h>

int main(void)
{
 FILE *fo, *fi;
 
 int32_t num = 439041101;
 int32_t res = 0;
 size_t len = sizeof (int32_t);
 
 fo = fopen("./test.bin", "w+b");
 fwrite(&num, 1, len, fo); /* jep, das wars schon */
 fclose(fo);
 
 fi = fopen("./test.bin", "rb");
 fread(&res, 1, len, fi); /* auch hier, einfach und effizient */
 fclose(fi);
 
 printf("geschrieben: %d, gelesen %d\n", num, res);
 return 0;
}