ATOF produces only 0.00

Projects Programming
1

Before I include a function into my sketch I am trying it in a sep. sketch to test it. So I wrote this to test the atof function:

char X = "123.45\0"; // String1
char Y = "0.67\0";  // String2

void setup() {
  Serial.begin(9600);
  delay(500);
  float x = atof(X);
  float y = atof(Y);
  int sX = sizeof(X);
  int sY = sizeof(Y);

  Serial.println("Ready");
  Serial.print("x = "); Serial.println(x);
  Serial.print("y = "); Serial.println(y);
  Serial.print("Sx= "); Serial.println(sX);
  Serial.print("Sy= "); Serial.println(sY);
}

void loop() {
}

But all it produces are zero's, why??

2

Don't you trust the compiler to terminate the string for you?
Didn't you get any warnings?

3

Define the character arrays properly. Note the square brackets.

char X[] = "123.45";

4

Hi, try this code:

char X[] = "123.45"; // String1
char Y[] = "0.67";  // String2
//String K = "123.45";
void setup() {
  Serial.begin(9600);
  delay(500);
  float x = atof(X);
  float y = atof(Y);
  int sX = sizeof(X);
  int sY = sizeof(Y);

  Serial.println("Ready");
  Serial.print("x = "); Serial.println(x);
  Serial.print("y = "); Serial.println(y);
  Serial.print("Sx= "); Serial.println(sX);
  Serial.print("Sy= "); Serial.println(sY);
}

void loop() {
}

ref: C library function - atof()

5

I'm surprised this produces zeroes.

6

X is char
sizeof(X) is 1

Iā€™m turning my phone upside down, moving it far and close and that 1 does not look like a 0 no matter what I do, help!

7

Didn't you notice the dire warnings?

If you ever get unexpected results from a sketch, set "Verbose messages during: [X] compilation" in Preferences and look for compiler warnings.

/Users/john/Documents/Arduino/sketch_jan06b/sketch_jan06b.ino:1:10: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 char X = "123.45\0"; // String1
          ^~~~~~~~~~
/Users/john/Documents/Arduino/sketch_jan06b/sketch_jan06b.ino:2:10: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 char Y = "0.67\0";  // String2
          ^~~~~~~~
/Users/john/Documents/Arduino/sketch_jan06b/sketch_jan06b.ino: In function 'void setup()':
/Users/john/Documents/Arduino/sketch_jan06b/sketch_jan06b.ino:8:19: warning: invalid conversion from 'char' to 'const char*' [-fpermissive]
   float x = atof(X);
                   ^
In file included from /Users/john/Library/Arduino15/packages/arduino/hardware/avr/1.8.4/cores/arduino/Arduino.h:23:0,
                 from sketch/sketch_jan06b.ino.cpp:1:
/Users/john/Library/Arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/avr/include/stdlib.h:361:15: note:   initializing argument 1 of 'double atof(const char*)'
 extern double atof(const char *__nptr);
               ^~~~
/Users/john/Documents/Arduino/sketch_jan06b/sketch_jan06b.ino:9:19: warning: invalid conversion from 'char' to 'const char*' [-fpermissive]
   float y = atof(Y);
                   ^
In file included from /Users/john/Library/Arduino15/packages/arduino/hardware/avr/1.8.4/cores/arduino/Arduino.h:23:0,
                 from sketch/sketch_jan06b.ino.cpp:1:
/Users/john/Library/Arduino15/packages/arduino/tools/avr-gcc/7.3.0-atmel3.6.1-arduino7/avr/include/stdlib.h:361:15: note:   initializing argument 1 of 'double atof(const char*)'
 extern double atof(const char *__nptr);
               ^~~~
1 Like
8

Oops! I meant "Compiler warnings: [All]". That is something you should turn on and leave on. The "Show verbose output" options are better for upload errors.

9

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