Converting from C: fputc and fwrite in C#?

Question

Question: In order to write a C# interface to libespeak, I need to convert the callback SynthCallback to C#.

See the below C code.
You might need this for reference:
https://ccrma.stanford.edu/courses/422/projects/WaveFormat/
http://www-mmsp.ece.mcgill.ca/documents/audioformats/wave/wave.html

Basically,

espeak_initialize
espeak_SetSynthCallback(SynthCallback);
espeak_SetParameter(espeakRATE, 510, 0);        
espeak_Synth(".", 20, 0, POS_CHARACTER, 0, 0, NULL, NULL);

are DllImport-ed function. And I already have them working asynchronously, without file.

Now I want to get the synchronous version working with files, but I have a little problem:

The callback function

static int SynthCallback(short *wav, int numsamples, espeak_EVENT *events)

First, I need to create a delegate for that I can pass this function to the C dll/so. Which isn't a problem, but if I make short *wav to a System.IntPtr, how do I write the data to a file ?

In other words: Can somebody help me with fwrite, fputc, Write4Bytes converting this into proper C#?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <espeak/speak_lib.h>

// gcc -o mine speak.cpp -I/usr/include/espeak/ -lespeak


FILE *f_wavfile = NULL;

static int SynthCallback(short *wav, int numsamples, espeak_EVENT *events);


// Write 4 bytes to a file, least significant first
static void Write4Bytes(FILE *f, int value)
{
    int ix;

    for(ix=0; ix<4; ix++)
    {
        fputc(value & 0xff,f);
        value = value >> 8;
    }
}



int OpenWavFile(char *path, int rate)
{
    static unsigned char wave_hdr[44] = {
        'R','I','F','F',0x24,0xf0,0xff,0x7f,'W','A','V','E','f','m','t',' ',
        0x10,0,0,0,1,0,1,0,  9,0x3d,0,0,0x12,0x7a,0,0,
        2,0,0x10,0,'d','a','t','a',  0x00,0xf0,0xff,0x7f
    };


    if(path == NULL)
        return(2);

    if(path[0] == 0)
        return(0);

    if(strcmp(path,"stdout")==0)
        f_wavfile = stdout;
    else
        f_wavfile = fopen(path,"wb");

    if(f_wavfile == NULL)
    {
        fprintf(stderr,"Can't write to: '%s'\n",path);
        return(1);
    }


    fwrite(wave_hdr, 1, 24, f_wavfile);
    Write4Bytes(f_wavfile, rate);
    Write4Bytes(f_wavfile, rate * 2);
    fwrite(&wave_hdr[32], 1, 12, f_wavfile);
    return(0);
}   //  end of OpenWavFile



static void CloseWavFile()
{
    unsigned int pos;

    if((f_wavfile==NULL) || (f_wavfile == stdout))
        return;

    fflush(f_wavfile);
    pos = ftell(f_wavfile);

    fseek(f_wavfile, 4, SEEK_SET);
    Write4Bytes(f_wavfile, pos - 8);

    fseek(f_wavfile, 40, SEEK_SET);
    Write4Bytes(f_wavfile, pos - 44);

    fclose(f_wavfile);
} // end of CloseWavFile


int main() 
{   
    char buf[22050];
    int i = 0;
    memset(&buf, 0, sizeof(buf));
    // OpenWavFile((char*) "test.wav", 22050);
    int SampleRate = espeak_Initialize(AUDIO_OUTPUT_SYNCHRONOUS, 300, NULL, 0);

    OpenWavFile((char*) "test.wav", SampleRate);

    espeak_SetSynthCallback(SynthCallback);
    //espeak_SetParameter(espeakRATE, 510, 0);
    //espeak_SetParameter(espeakRANGE, 75, 0);
    for (i=0; i < 9;i++) 
    {
        /*
        espeak_ERROR espeak_Synth(
            const void *text,
            size_t size,
            unsigned int position,
            espeak_POSITION_TYPE position_type,
            unsigned int end_position,
            unsigned int flags,
            unsigned int* unique_identifier,
            void* user_data);
        */
        //espeak_POSITION_TYPE.POS_CHARACTER
        espeak_Synth("test", 10, 0, POS_CHARACTER, 0, 0, NULL, NULL);
        fwrite(buf, 1, 5512, f_wavfile);
        espeak_Synth(".", 20, 0, POS_CHARACTER, 0, 0, NULL, NULL);
        fwrite(buf, 1, 22050, f_wavfile);
    }
    CloseWavFile();
}


static int SynthCallback(short *wav, int numsamples, espeak_EVENT *events)
{
    if (wav == NULL) 
        return 0;

    if (numsamples > 0) 
    {
        fwrite(wav, numsamples * 2, 1, f_wavfile);
    }

    return 0;
}

score 2 · Accepted Answer · answered Jul 03 '11 at 17:00

2

FileStream sink;
Int32 SynthCallback(IntPtr wav, Int32 numsamples, IntPtr events)
{
    var wavm = new Int16[numsamples];
    Marshal.Copy(wav, wavm, 0, numsamples);
    // and do something with wavm

    //or
    var wavbytes = new Byte[numsamples * 2];
    Marshal.Copy(wav, wavbytes, 0, numsamples*2);
    sink.Write(wavbytes, 0, numsamples*2);
}

For writing 32-integers, you can either use BitConverter.GetBytes and FileStream.Write or maybe BinaryWriter.

answered Jul 03 '11 at 17:00

Ben Voigt

277,958
43
419
720

I was amazed, success at the first attempt, with BinaryWriter + BitConverter.GetBytes. – Stefan Steiger Jul 04 '11 at 00:19

score 0 · Answer 2 · answered Jul 03 '11 at 16:23

0

You could P/Invoke CreateFile/WriteFile to write the IntPtr directly.

answered Jul 03 '11 at 16:23

Goz

61,365
24
124
204

That requires the function to be exported, which it isn't, plus it doesn't make sense to call from managed to unmanaged, to managed callback, and from there back to unmanaged code... – Stefan Steiger Jul 03 '11 at 16:33
@Quandary: Well then you need to copy the data in the IntPtr into a short[]. – Goz Jul 03 '11 at 16:34

Converting from C: fputc and fwrite in C#?

2 Answers2