Convert text array/buffer to integer and string.

hi! i'm sending text to an arduino and the output of that library is a uint8_t array.

Atm the text send is a number between "0" and "1023"

void something(uint8_t * text){
 analogWrite(13,text);// does not work
toInt() also not
int() not
atoi() not
invalid conversion from 'uint8_t* {aka unasigned char*}' to 'const char*'

i need to convert it to an integer or better to a uint16_t.

As i plan to send custom commands in near future it would also be good to know how to convert that array to a string, that i then split/manipulate/parse.. whatever.

i looked in various posts but i couldn't get it to work on that simple example above. i'm new to c++

if it's needed the length is also aviable inside the function.

3 Answers 3


Your problem is that you are storing your text in an unsigned pointer (uint8_t *)instead of a signed pointer (char *).

If you change all your text types to char * then you can directly use atoi(). If you have a lot to change, though, you can just cast the unsigned pointer into a signed one (and make it const at the same time):

analogWrite(13, atoi((const char *)text));
  • its from a websocket lib... i would need to rewriter the whole lib...anyway this worked perfectly
    – cocco
    Commented Nov 15, 2015 at 13:20
  • btw i will update this analogwrite at 60Hz . is "cast" slow/are there faster ways to convert the buffer to a string or int?
    – cocco
    Commented Nov 15, 2015 at 13:35
  • @cocco Cast makes no difference at runtime, only compile time. There are faster ways to convert than atoi, but they aren't as safe - i.e., they don't do any bounds checking.
    – Majenko
    Commented Nov 15, 2015 at 13:36
  • it works but i have a bigger problem now. it crashes really fast. i can't send data faster than 2 times per second. maybe you know more about this.arduino.stackexchange.com/questions/17811/esp8266-websockets
    – cocco
    Commented Nov 16, 2015 at 10:25

analogWrite is a function to set a PWM duty cycle value to a pin on the micro

Usually to control a motor speed or LED brightness or similar.

Unless you plan to use the char value to set the PWM value??

A bit more context would help with your problem.

  • i control a led with websockets. now it works. @Majenko answered it correctly
    – cocco
    Commented Nov 15, 2015 at 13:28
  • This isn't really an answer. Commented Oct 31, 2016 at 23:03

I've converted first four bytes to string, and then to int :

void something(uint8_t * payload){
String str="";
char c;
for(int i=0;i<4;i++)
    if (isDigit(c=(char)(*(payload+i))))
        str += c;

int Val =str.toInt();

  • This is a very inefficient approach. Commented Oct 31, 2016 at 23:03

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