Can't use uint16_t in library

Question

I wonder why the following minimal example sketch doesn't compile (unknown type name 'uint16_t'):

sketch_does_not_compile.ino:

#include "myheader.h"
void setup() {
 char a[]="hello world";
 uint16_t l=str_len(a);
 Serial.println(l);
}
void loop() {}

myheader.c:

uint16_t str_len(char* input_string) {
 uint16_t i=0;
 while (input_string[i++]!='0円');
 return i;
}

myheader.h:

#include "myheader.h"
uint16_t str_len(char* input_string);

Compilation fails with:

myheader.c: At top level:
myheader.c:3:1: error: unknown type name 'uint16_t'
 uint16_t str_len(char* input_string);
 ^
exit status 1
unknown type name 'uint16_t'

Using uint16_t in the .ino-file directly like in the sketch below compiles fine.

sketch_compiles.ino:

uint16_t str_len(char* input_string) {
 uint16_t i=0;
 while (input_string[i++]!='0円');
 return i;
}
void setup() {
 char a[]="hello world";
 uint16_t l=str_len(a);
 Serial.println(l);
}
void loop() {}

What am I missing?

• Juraj: #include <stdint.h>
• ocrdu: Why is the declaration of str_len() in the .c file and the implementation in the .h file?

Answer 1

Using #include <Arduino.h> in your myheader.h will also include <stdint.h> and probably solve this.

The Arduino IDE automatically includes Arduino.h in the sketch itself, but apparently not for external stuff.