Problems with printf () on AVR in C floating point

I am going back to C and I was working on an "academic" exercise to sharpen some old skills again. My project revolves around a fairly simple sine generation process. I started just coding x86 on the command line (Fedora Core 20) and everything worked fine. Then I ported the code into AVR and I started to learn a lot. For example how to configure the UART as stdout. However, since sines are floating point, I ran into problems using printf and sprintf.

The program generates 30 sines and then outputs the values ​​to the terminal. The text "Sine:" prints correctly, but then I get question marks for the float. Replacing a variable with a constant had no effect.

The first thing I was suggested was if I remembered the linker option for full floating point support - indeed, I forgot. Again, adding this to my makefile had no effect.

I'm not sure about the copy and paste policy of the code: should I paste it and my makefile here to check?

EDIT: Sorry for the long delay. I did some more reading, including what the first answer is related to. I already read this link before (GNU one) and I included the link in my Makefile, which is why I am so confused. Here's my Makefile in all its glory:

P               = sines
OBJ             = sines.o
PROGRAMMER      = buspirate
PORT            = /dev/ttyUSB0
MCU_TARGET      = atmega328p
AVRDUDE_TARGET  = atmega328p
HZ              = 16000000
DEFS            =
LIBS            = -lprintf_flt -lm
CC              = avr-gcc

override CFLAGS = -g -DF_CPU=$(HZ) -Wall -O1 -mmcu=$(MCU_TARGET) $(DEFS)
override LDFLAGS= -Wl,-Map,$(P).map -u,vfprintf

OBJCOPY     = avr-objcopy
OBJDUMP     = avr-objdump

all: $(P).elf lst text

$(P).elf: $(OBJ)
    $(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ $(LIBS)

clean:
    rm -rf *.hex *.bin *.map *~ sine*.csv *.o $(P).elf *.lst

lst: $(P).lst

%.lst: %.elf
    $(OBJDUMP) -h -S $< > $@

text: hex bin

hex: $(P).hex
bin: $(P).bin

%.hex: %.elf
    $(OBJCOPY) -j .text -j .data -O ihex $< $@

%.bin: %.elf
    $(OBJCOPY) -j .text -j .data -O binary $< $@

install:  $(P).hex
    avrdude -p $(AVRDUDE_TARGET) -c $(PROGRAMMER) -P $(PORT) -v -U flash:w:$(P).hex 

      

        
        
        
      

    

What I'm worried about is that maybe the linker arguments are not in the correct order? From what I can tell, they are only ...

I'm sure my code itself is fine. If you like, I can post it here. Also, thanks for submitting my question here. Didn't quite understand the difference between them!

Here is the source code. It runs on ATmega328P. This current version prints the constant as debug, not the output from sinescalc (), although I know this function works (at least it should, I'm sure I checked with avr-gdb at some point - it definitely works on the command line as well as on the MSP430).

#include <avr/io.h>
//#include <util/delay.h>
#include <string.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>


static int uart_putchar(char c, FILE *stream);

static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);

static int uart_putchar(char c, FILE *stream) {
    if (c == '\n')
        uart_putchar('\r', stream);
    while(!(UCSR0A & (1<<UDRE0)));
    UDR0 = c;
    return 0;
}

void sinescalc(double *sinptr, int cycles, int size) {

    double pi = acos(-1);
    double step = ((pi * (cycles*2))/ size);

    float temp;
    double z = step;

    int y;
    for(y = 0; y<= size; y++) {
        temp = sin(z); // calculate the current sine
        *sinptr = (double)temp; // pass it into the array from main()
        z += step; // add the step value to prepare for next sine
        sinptr++; // should move the pointer by correct size of variable
    }
}

int main(void) {

    unsigned long _fosc = 16000000;
    unsigned int _baud = 19200;
    unsigned long _myubrr = _fosc/16/_baud-1;
    unsigned int array_size = 256;

    UBRR0L = (unsigned char)_myubrr;
    UCSR0B = (1<<RXEN0)|(1<<TXEN0); //enable receiver and transmitter

    stdout = &mystdout;
    double sines[array_size];
    double *sinepointer = sines; // set sinepointer to first element of sines array

    sinescalc(sinepointer, 2, array_size); // calculate two cycles of sine, with 255 data points

    int y;
    //char msg[6] = ("Sine: ");
    char output[40];

    for(y = 0; y <= array_size; y++) {
        sprintf(output, "Sine:\t %.6f", 1.354462);
        printf(output);
        printf("\n");
    }



    return 0;
}