问使用‘%f’和‘%f’的问题(Avr)

EN

void read_float_from_buffer(float *var, char *buffer, uint8_t start, uint8_t end) {
    char val_buf[8];

    // transfer characters representing float to a temporary buffer
    uint8_t p=0;
    for (uint8_t i=start;i<=end && p<7;i++) {
        val_buf[p++]=buffer[i];
    }
    val_buf[p]='\0';

    // perform sscanf on this temporary buffer
    float buf=-1;
    if(sscanf(val_buf, "%.2f", &buf)==1) // this fails, sscanf returns 0
      *var=buf;
}

float a_float_variable=0.;
void find_float_in_buffer(char *buffer) {
    uint8_t start,end=0;
    /*
    I do some magic here to find out where my float string starts and ends
    */
    read_buffer_float(&a_float_variable,buffer,start,end);
}

#define F_CPU 8000000UL

#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>
#include <util/delay.h>
#include "src/peripheral-core/uart.c"

int main() {
  _delay_ms(200);
  uart_init();
  uartWriteString("application started\n\r\0");

  char test[]="12.34\0";
  float testfloat=-1;
  sscanf(test, "%f", &testfloat);

  uartWriteString("teststring is:\t\0");
  uartWriteString(test);
  uartWriteString("\n\rscanned float is:\t\0");
  uartWriteFloat(testfloat);
  uartWriteString("\n\0");

  for (;;) {
    _delay_ms(1000);
  }
}

application started

teststring is:  12.34

scanned float is:   -1.000

avr-gcc -std=gnu99 -c -Os -Wall -mmcu=atmega168p main.c -o main.o
avr-gcc -std=gnu99 -Wl,-u,vfprintf -lprintf_flt -lm -mmcu=atmega168p main.o -o main.elf
avr-objcopy -O ihex -j .data -j .text main.elf main.hex

#include <stdio.h>

int main() {
  printf("application started\n\r\0");

  char test[]="12.34\0";
  float testfloat=-1;
  sscanf(test, "%f", &testfloat);

  printf("teststring is:\t\0");
  printf(test);
  printf("\n\rscanned float is:\t\0");
  printf("%.2f",testfloat);
  printf("\n\0");
}