Converting uint8_t buffer to complex float buffer in C++

Question

I am reading in a buffer of IQ data from a Software Defined Radio which I want to demodulate. The data I am receiving is a buffer of 8 bit unsigned int's. I need to convert this to buffer to type complex float for demodulation of the signal (I plan on using Liquid DSP Library). I am having difficulties in converting the buffer.

In GNURadio I have worked out my logic and am writing the output of my code to a binary file which I can then using as an input source for testing. So far the only thing that working is writing the uint8_t buffer to the file, other manipulation on the data breaks the logic.

Here is a snippet of the C++ code I have tried:

uint8_t buffer[buffersize];

uint8_t I;
uint8_t Q;

float Ifloat;
float Qfloat;

complex<float> complexsample;

ofstream myfile;
myfile.open("example.bin", ios::out | ios::app | ios::binary);

for (int x = 0; x < (buffersize/2); x++) {

    memcpy(&I, buffer + (2 * x), 1);
    memcpy(&Q, buffer + (1 + (2 * x)), 1);
    //writing I and Q above to a binary file works
        //myfile.write((char*) &I, sizeof(I));
        //myfile.write((char*) &Q, sizeof(Q));

    Ifloat = (float) I;
    Qfloat = (float) Q;
    //when I write Ifloat and Qfloat to a binary file then pass the 
    //file as an input source into the Add Const block things stop working
        //myfile.write((char*) &IIfloat, sizeof(Ifloat));
        //myfile.write((char*) &Qfloat, sizeof(Qfloat));


    Ifloat -= 127.0;
    Qfloat -= 127.0;
    //what I would do to turn the turn the unsigned value into a signed value
        //myfile.write((char*) &IIfloat, sizeof(Ifloat));
        //myfile.write((char*) &Qfloat, sizeof(Qfloat));

    complexsample.real(Ifloat);
    complexsample.imag(Qfloat);
    //what I would do to turn the I and Q floats into a single complex sample
        //myfile.write((char*) &complexsample, sizeof(complexsample));
}

Answer 1

DrPaulBrewer wrote a simple program to do the exact conversion I was looking for. The link to his GitHub is https://gist.github.com/DrPaulBrewer/917f990cc0a51f7febb5

His source code is:

void main(int argc, char *argv[])
{
int byte1, byte2; // int -- not unsigned char -- see fgetc man page
float _Complex fc;
const size_t fc_size = sizeof(fc);
FILE *infile,*outfile;
const float scale = 1.0/128.0;
const char *infilename = argv[1];
const char *outfilename = argv[2];
if (argc<3){
printf("usage: rtlsdr-to-gqrx infile outfile\n");
exit(1);
}
// printf("in= %s out= %s \n", infilename, outfilename);
infile=fopen(infilename,"rb");
outfile=fopen(outfilename,"wb");
if ((infile==NULL) || (outfile==NULL)){
printf("Error opening files\n");
exit(1);
}
while ((byte1=fgetc(infile)) != EOF){
if ((byte2=fgetc(infile)) == EOF){
exit(0);
}
fc = scale*(byte1-127) + I*scale*(byte2-127);
fwrite(&fc,fc_size,1,outfile);
}
}