Question

I need to send floating point numbers using a UDP connection to a Qt application. Now in Qt the only function available is

qint64 readDatagram ( char * data, qint64 maxSize, QHostAddress * address = 0, quint16 * port = 0 )

which accepts data in the form of signed character buffer. I can convert my float into a string and send it but it will obviously not be very efficient converting a 4 byte float into a much longer sized character buffer.

I got hold of these 2 functions to convert a 4 byte float into an unsinged 32 bit integer to transfer over network which works fine for a simple C++ UDP program but for Qt I need to receive the data as unsigned char.

Is it possible to avoid converting the floatinf point data into a string and then sending it?

uint32_t htonf(float f)
{
    uint32_t p;
    uint32_t sign;

    if (f < 0) { sign = 1; f = -f; }
    else { sign = 0; }

    p = ((((uint32_t)f)&0x7fff)<<16) | (sign<<31); // Whole part and sign.
    p |= (uint32_t)(((f - (int)f) * 65536.0f))&0xffff; // Fraction.

    return p;
}

float ntohf(uint32_t p)
{
    float f = ((p>>16)&0x7fff); // Whole part.
    f += (p&0xffff) / 65536.0f; // Fraction.

    if (((p>>31)&0x1) == 0x1) { f = -f; } // Sign bit set.

    return f;
}

Answer 1

Not sure why the downvote, since the question is vague in requirements.

A 4-byte float is simply a 4 character buffer, if cast as one. If the systems are homogenous, the float can be sent as a signed char *, and bit for bit it’ll be the same read into the signed char * on the receiver directly, no conversion needed. If the systems are heterogenous, then this won’t work and you need to convert it to a portable format, anyway. IEEE format is often used, but my question is still, what are the requirements, is the float format the same between systems?