ESP8266 Community Forum

- Sun Dec 04, 2016 10:57 pm #59111 Posted to https://github.com/esp8266/Arduino/issues/2515 back in September but no response so will try here.

Basic Infos

Hardware

Hardware: ?ESP-12?
Core Version: ?2.1.0-rc2?

Description

Problem description

Settings in IDE

Module: Adafruit HUZZAH ESP
Flash Size: ?4MB/1MB?
CPU Frequency: ?80Mhz?
Flash Mode: ?qio?
Flash Frequency: ?40Mhz?
Upload Using: ?OTA / SERIAL?
Reset Method: ?ck / nodemcu?

Sketch

Code: Select all#include <stdlib.h>
#include <math.h>
#include <Arduino.h>

void setup() {
    Serial.begin(9600);
    while (!Serial);

    char *sci = "1.0e-7";
    Serial.println (sci);
    Serial.println (1e7*atof(sci));

}

void loop() {

}


Debug Messages

messages here
Output is:

1.0e-7
10000000.00

should be
1.0e-7
1.00

I also tried

Code: Select allSerial.println (strtod(sci,(char**)NULL));

but same result.

Thanks.

- Mon Jan 02, 2017 4:27 pm #60285 Ï've noted tbe same problem for the ESP8266-based Digistump Oak - more details at https://digistump.com/board/index.php/topic,2531.0.html. Will post here if I come up with a solution.

- Thu Jan 05, 2017 8:35 pm #60511 I've taken the code for strtod (alias for atof) and modified it to create function atof_e.

I had initially modified strtod so both atof and strtod would work properly - but this would require more work for someone else if they wish to use this code: you'd have to find and modify the appropriate library. Also, if I or someone else later updates to a newer version of the library the modification might well be overwritten with the old bugged version, and I/you will probably have forgotten about this modification.

Usage for the modified function:

double atof_e (const char* str);

Identically to atof(), atof_e() parses the string str, interpreting its content as a floating point number and returns its value as a double. As per the C++ 98 specification, it may optionally followed by an exponent part (an e or E character followed by an optional sign and a sequence of digits).

Code: Select alldouble atof_e(const char* str) {
    char ** endptr;
    double result = 0.0;
    double factor = 1.0;
    bool exp_factor = 1;      //default 1 - positive exponent. Use 0 for negative
    double exponent = 0;
    double multiplier = 1;    //multiplier for exponent
    bool decimals = false;
    char c;

    while(isspace(*str)) {
        str++;
    }

    if(*str == 0x00) {
        // only space in str?
        if (endptr) *endptr = (char*) str;
        return result;
    }

    if(*str == '-') {
        factor = -1;
        str++;
    } else if(*str == '+') {
        str++;
    }

    while((c = *str)) {
        if(c == '.') {
            decimals = true;
            str++;
            continue;
        }

        if (c == 'e' || c == 'E') {
            str++;
            if(*str == '-') {
                exp_factor = 0;
                str++;
            } else if(*str == '+') {
                str++;
            }
            while (c = *str) {      //this while loop for the exponent
                int d = c - '0';
                if (d < 0 || d > 9) {
                    break;
                }
                exponent = exponent * 10 + d;
                str++;
            }
        }
       
        else {
          int d = c - '0';
          if(d < 0 || d > 9) {
              break;
          }
 
          result = 10.0 * result + d;
          if(decimals) {
              factor *= 0.1;
          }
 
          str++;
        }
    }
    if (endptr) *endptr = (char*) str;
    result *= factor;

    if (exponent) {
      multiplier = pow(10, exponent);
      if (exp_factor) result *= multiplier;
      else result /= multiplier;
    }

    return result;
}