How do I convert a value from host byte order to little endian?

by

Here is an article about endianness and how to determine it from IBM:

Writing endian-independent code in C: Don’t let endianness “byte” you

It includes an example of how to determine endianness at run time ( which you would only need to do once )

const int i = 1;
#define is_bigendian() ( (*(char*)&i) == 0 )

int main(void) {
    int val;
    char *ptr;
    ptr = (char*) &val;
    val = 0x12345678;
    if (is_bigendian()) {
        printf(“%X.%X.%X.%X\n", u.c[0], u.c[1], u.c[2], u.c[3]);
    } else {
        printf(“%X.%X.%X.%X\n", u.c[3], u.c[2], u.c[1], u.c[0]);
    }
    exit(0);
}

The page also has a section on methods for reversing byte order:

short reverseShort (short s) {
    unsigned char c1, c2;

    if (is_bigendian()) {
        return s;
    } else {
        c1 = s & 255;
        c2 = (s >> 8) & 255;

        return (c1 << 8) + c2;
    }
}

;

short reverseShort (char *c) {
    short s;
    char *p = (char *)&s;

    if (is_bigendian()) {
        p[0] = c[0];
        p[1] = c[1];
    } else {
        p[0] = c[1];
        p[1] = c[0];
    }

    return s;
}

More Related Contents:

  1. How do I convert between big-endian and little-endian values in C++?
  2. Detecting endianness programmatically in a C++ program
  3. C/C++: Force Bit Field Order and Alignment
  4. Why does optimisation kill this function?
  5. 64 bit ntohl() in C++?
  6. Is there any “standard” htonl-like function for 64 bits integers in C++?
  7. Building a 32-bit float out of its 4 composite bytes
  8. Converting float values from big endian to little endian
  9. Floating point Endianness?
  10. What exactly is nullptr?
  11. Is #pragma once a safe include guard?
  12. Which, if any, C++ compilers do tail-recursion optimization?
  13. Create Random Number Sequence with No Repeats
  14. Define preprocessor macro through CMake?
  15. How should I deal with mutexes in movable types in C++?
  16. How to get std::vector pointer to the raw data?
  17. Is it possible to program iPhone in C++
  18. C++ How to detect Windows 10
  19. May I take the address of the one-past-the-end element of an array? [duplicate]
  20. Using C Libraries for C++ Programs
  21. c++ lambdas how to capture variadic parameter pack from the upper scope
  22. Why does valgrind say basic SDL program is leaking memory?
  23. Array decay to pointers in templates
  24. Why does libc++’s implementation of std::string take up 3x memory as libstdc++?
  25. Waiting for multiple futures?
  26. Why was std::pow(double, int) removed from C++11?
  27. What does “cv-unqualified” mean in C++?
  28. Immediate exit of ‘while’ loop in C++ [closed]
  29. Making my own photo-mosaic app with Qt using C++
  30. How can a char pointer be initialized with a string (Array of characters) but an int pointer not with an array of integer? [duplicate]

Leave a Comment