将 void* 转换为 memcpy 以获取浮点值

Question

Here is an example of the problem I'm trying to solve I get a buffer from the microphone and try and process it content. as kindly guided from this question Im trying to convert a char* to float*

the logic I declare a vector to hold my desired float then resize it to that of ArBuffer() and then copy to the vector.

ArBuffer() is a void gonna have to cast this to memcpy?

#include "Lib_api.h"
#include <alsa/asoundlib.h>
#include <stdio.h>
#include "audiorecorder.h"
#include "Globals.h"
#include <iostream>
#include <inttypes.h>
#include <string.h>
#include <stdlib.h>
#include <vector>
#include <cstring>

using namespace std;

//Declare Creation
void* mCore;

int main(void)
{
    // recorder
    int rc;
    int mode = 3;
    const float sampleRate = 44100; //max 22Hz
    int bufferSize = 1024; //Check this should be good 1024

    //initialise
    mCore = OXY_Create();

    //initialise audio recorder
    rc = arInitialise();

    OXY_Configure(mode, sampleRate, bufferSize, mCore);
    //initialise check hardware
    if(rc)
    {
        std::cerr << "Fatal error: Audio could not be initialised" << rc << std::endl <<std::endl;
        arFree();
        exit(1);
    }

    //start recording
    rc = arStartRecording();

    //application loop
    while(arIsRunning())
    {
        //declare vector
        std::vector<float> values;

        //resize values to size of arbuffersize
        values.resize(arBufferSize(), sizeof(float));
        //arBufferSize()/sizeof(float);

       //need to cast this arBuffer() to memcpy?

        std::memcpy(arBuffer(), &values[0], sizeof(values[0]));

        // values[0] this will hold the latest data from the microphone?
        int ret = OXY_DecodeAudioBuffer(&values[0], values.size(), mCore);

        if (ret == -2)
        {
        std::cerr << "FOUND_TOKEN ---> -2 " << std::endl << std::endl;
        }
            else if(ret>=0)
        {

        std::cerr << "Decode started ---> -2 " << ret << std::endl << std::endl;
        }
        else if (ret == -3)
        {
        //int sizeStringDecoded = OXY_GetDecodedData(mStringDecoded, mCore);

         std::cerr << "STRING DECODED ---> -2 " << std::endl << std::endl;
         // ...
        }
        else
        {
          std::cerr << "No data found in this buffer" << std::endl << std::endl;
            //no data found in this buffer
        }
    }

    //Clean up
    arFree();

  return 0;
}

I change the format to SND_PCM_FORMAT_FLOAT_LE from SND_PCM_FORMAT_S16_LE as kindly suggested from another SO question.

* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API

#include <stdlib.h>
#include <alsa/asoundlib.h>
#include <pthread.h>
#include "settings.h"
#include "audiorecorder.h"


pthread_t thr;
pthread_mutex_t mutex;
snd_pcm_t *handle;
snd_pcm_uframes_t frames;
unsigned char* buffer;
BOOL running;
size_t buffersize;


BOOL arIsRunning(void)
{
    return running;
}


void arAcquireBuffer(void)
{
    //printf("Acquired buffer\n");
    pthread_mutex_lock(&mutex);
}


void arReleaseBuffer(void)
{
    //printf("Released buffer\n");
    pthread_mutex_unlock(&mutex);
}


const unsigned char* arBuffer(void)
{
    return buffer;
}


const size_t arBufferSize(void)
{
    return buffersize;
}


void* entry_point(void *arg)
{
    int rc;

    fprintf(stderr, "Listening...\n");

  while (running)
    {
        arAcquireBuffer();
    rc = snd_pcm_readi(handle, buffer, frames);

    //stream to stdout - useful for testing/debugging
    //write(1, buffer, buffersize);
        arReleaseBuffer();

    if (rc == -EPIPE) {
      /* EPIPE means overrun */
      fprintf(stderr, "overrun occurred\n");
      snd_pcm_prepare(handle);
    }
        else if (rc < 0) {
      fprintf(stderr, "error from read: %s\n", snd_strerror(rc));
            running = FALSE;
    }
        else if (rc != (int)frames) {
      fprintf(stderr, "short read, read %d frames\n", rc);
    }
 }

    return NULL;
}



int arInitialise(void)
{
  snd_pcm_hw_params_t *params;
  unsigned int val;
  int rc, dir;

    running = FALSE;

  /* Open PCM device for recording (capture). */
  rc = snd_pcm_open(&handle, RECORDER_DEVICE, SND_PCM_STREAM_CAPTURE, 0);
  if (rc < 0) {
    fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc));
    return rc;
  }
    else
    {
        fprintf(stderr, "Successfully opened default capture device.\n");
    }

  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(&params);

  /* Fill it in with default values. */
  snd_pcm_hw_params_any(handle, params);

  /* Set the desired hardware parameters. */

  /* Interleaved mode */
  snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);

  /* Signed 16-bit little-endian format */
  snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_FLOAT_LE)


  /* Channels */
  snd_pcm_hw_params_set_channels(handle, params, NUM_CHANNELS);
    fprintf(stderr, "Channels set to %d.\n", NUM_CHANNELS);


  /* sampling rate */
  val = SAMPLE_RATE;
  snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
    fprintf(stderr, "Samplerate set to %d.\n", val);

  /* Set period to FRAMES_PER_BUFFER frames. */
  frames = FRAMES_PER_BUFFER;
  snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);

  /* Write the parameters to the driver */
  rc = snd_pcm_hw_params(handle, params);
  if (rc < 0) {
    fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc));
    return rc;
  }

  /* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params, &frames, &dir);
  buffersize = frames * 2 * NUM_CHANNELS; /* 2 bytes/sample * channels */
  buffer = (unsigned char*) malloc(buffersize);

  /* We want to loop forever */
  //snd_pcm_hw_params_get_period_time(params, &val, &dir);

  return 0;
}


int arStartRecording(void)
{
    if(running) return 1;

  if(pthread_mutex_init(&mutex, NULL))
  {
    printf("Unable to initialize mutex\n");
    return -1;
  }

  if(pthread_create(&thr, NULL, &entry_point, NULL))
  {
    fprintf(stderr, "Could not create recorder thread!\n");
        running = FALSE;
    return -1;
  }

    running = TRUE;
    return 0;
}


void arStopRecording(void)
{
    running = FALSE;
}


void arFree(void)
{
    running = FALSE;
    sleep(500);
  snd_pcm_drain(handle);
  snd_pcm_close(handle);
  pthread_mutex_destroy(&mutex);
  free(buffer);
}

Answer 1

values.resize(arBufferSize(), sizeof(float))

Well, that wasn't what I wrote in the other comment. You need to divide the buffersize (in bytes) by the number of bytes per float to get the number of floats: arBufferSize() / sizeof(float)

std::memcpy(arBuffer(), &values[0], sizeof(values[0]));

memcpy for historical reasons has its destination and source reversed. The const* error is because you're asking memcpy to write to arBuffer .

Also, sizeof(values[0]) is the size of one float, in bytes. You already have arBufferSize() , which is exactly the size that memcpy needs.