Questions tagged [c-string]
A "C string" is an array of characters that ends with a 0 (null character) byte. The array, not any pointer, is the string.
28
questions
15
votes
1
answer
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Convert int to char[]
I'm looking to convert an int value to a char array. currently I've found the following will return [number]
int num = [number]
str = String(num);
str.toCharArray(cstr,16);
Serial.println(cstr);
...
- 923
12
votes
6
answers
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views
Using String instead of C string, yet another attempt to touch a loaded issue
I've been reading a lot over the years why we should not use the notorious String class and how heap fragmentation is bad practice and not professional and we should never use it in our programs or we'...
- 411
10
votes
5
answers
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formatting strings in Arduino for output
I wander what is the best option for formatting strings in Arduino for output.
I mean what's a preferable way in the point of view of performance, memory usage – things like that.
I see, people ...
- 439
3
votes
2
answers
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views
Problems on convert byte[] to String
I'm reading a RFID Card from RC522 and send the data to my computer. My problem is the conversion of byte[] to String or std::string.
#define SIZE_BUFFER 18
#define MAX_SIZE_BLOCK 16
byte ...
- 131
2
votes
1
answer
2k
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Using c_str() on String for IPAddress with NTPClient provides wrong values
Libraries
NTPClient
Board
Olimex ESP32-POE board
Behaviour
I have written a code that connects the board to a local NTP Server (which is an embedded board). I tried assigning the IP Address of ...
- 179
1
vote
1
answer
250
views
Yet another basic and silly question about C++ strings
I made a sketch like this:
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
char str1[64] = "test with spaces";
char str2[32] = "test with spaces";
Serial....
- 61
1
vote
2
answers
2k
views
strcmp doesn't seem to work
I'm trying to compare a char array that I'm assembling to a string and I'm having trouble comparing the strings.
I'm getting the data for the char array as a set of bytes and I'm compiling it into a ...
- 357
1
vote
2
answers
840
views
Arduino - Function -> return Cstr instead of string
I have following function for my Arduino:
String readLine() {
String received = "";
char ch;
while (myFile.available()) {
ch = myFile.read();
if (ch == '\n' or ch == '\r') {
...
- 125
1
vote
1
answer
316
views
Parse char* mac-string to uint8_t array
I have to handle a String coming in over UART containing a bunch of information, part of it is a MAC-address that I get by using String.substring(a, b) returning a 12-char String representing a mac-...
- 11
1
vote
2
answers
7k
views
Read Comma Separated String
I have a string that looks like this "10.00,20.00,-50.00," in which these are angle values and they have 2 decimals and can be negative. I want to separate them into 3 separate floats. Here ...
1
vote
2
answers
267
views
When Writing Library, return String or return char *
I am trying to write my own Arduino library and I would like to make it useful not just for ESP32/ESP8266 boards but also with Arduino boards.
I have created my header file like this
test.cpp
#...
- 223
1
vote
1
answer
4k
views
Char* and string conversion from an ESP8266 web server
I have the following Arduino code for configuring a wifi connection through a simple webpage:
I declare char* ssid;. Later I read a value from a SPIFFS config file where q_ssid is declared as a ...
1
vote
0
answers
414
views
Conversion from string to char array
I know this is Arduino Forum but I think this question is related to programming, I am using ESP8266 for the project. I need to convert the string incoming on the serial through UART lines and ...
- 11
0
votes
2
answers
4k
views
Max length of char arrays?
I'm running the following Sketch on my Arduino Uno:
const boolean verbose = true;
void debug(const char *s){
if(verbose){
char buf[8 + sizeof(s)] = "[DEBUG] ";
strcat(buf, s);
...
- 117
0
votes
2
answers
187
views
String() vs char for simple flow control
I am newbie in Arduino and writing a program where I want to control the flow by using Serial monitor input (PI controller).
I've read that using String() although easier it is slower than using char. ...
0
votes
3
answers
2k
views
How to replace String objects with char arrays while still using string methods
I am running the following code on my ESP8266 (AI-Thinker ESP8266MOD).
I send an HTTP GET request and a pin is set to high for a 1/2 second.
However, after some time (sometimes 1hr, 2hrs, 12hrs, ...
- 167
0
votes
2
answers
521
views
Does toCharArray prevent a String being created on the heap?
I know it's bad to use Strings due to the memory problems that can occur.
I've tried to remove all instances of strings from my code.
But I'm not sure about this line:
http.getString().toCharArray(...
- 167
0
votes
1
answer
142
views
String operations printing random character on Serial Monitor
I want to extract the file name MyFile.txt out of a path which is stored in a string "C:\\MyDirectory\\MyFile.txt";
I found a simple c code which does the job.
string filename = "C:\\...
0
votes
1
answer
784
views
Reading bits from a const char pointer
I'm getting a bit tripped up on const char pointers lately.
I'm getting a message from a server that comes through as either a c style string, a standard library string, or a WString:
I'm sending ...
- 357
0
votes
1
answer
79
views
Any explanation for this behavior?
For the below code snippet
const char* fr_fbdb(char tag[30]) // fn for retrieving data
{
char full_path[120];
const char *_dt ;
strcpy(full_path , base_path);
strcat(full_path , tag);
...
0
votes
1
answer
61
views
declaration of 'varDay' as array of references error
I am trying to write a function to store the date and time data from an RTC module. I have used char arrays to implement the function. I get "declaration of 'varDay' as array of references" ...
- 183
0
votes
1
answer
3k
views
Convert JSON into string for MQTT
I am trying to publish json object into string with following snippet
JSONVar data;
data["chipid"] = chipId;
data["co2_equivalent"] = co2_equivalent.c_str();
data["tvoc"] = tvoc.c_str();
data["...
- 113
0
votes
1
answer
655
views
Mqtt not subscribe on topic that's converted from String to char array
I am still not sure what should be the exact Title for this question, because I don't know where the problem is.
I am using #include <MQTTClient.h> mqtt library to subscribe on a topic.
This ...
- 191
0
votes
2
answers
3k
views
Arduino GSM module + SMS string sending garbage value
I want to check the water level and have an SMS sent via a GSM module. Reed switches are connected to four Arduino analog inputs.
I am unable to add a string and tank level (TKLVL) in program.
The ...
- 41
0
votes
1
answer
1k
views
Store 3-dimensional char array in program memory with PROGMEM
I'm running a sketch whith a quite big, constant three dimensional char array (or simply, a table of strings). As this takes lots of RAM I'd like to store it in programm memory in order to keep the ...
- 117
0
votes
1
answer
216
views
snprintf doesn't display float values
I don't understand why the formatted string is displaying ?? instead of float values.
My code:
#include <Arduino.h>
#include <Wire.h>
#include "SparkFunCCS811.h"
#include <...
- 183
0
votes
1
answer
3k
views
Splitting a Serial.readString into string array
I am working on a project where I need to split incoming data from serial (time to be exact, so aa:bb:cc) and need to split it into aa then bb and cc, ideally into an array. I know I could use ...
- 35
-1
votes
1
answer
864
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Reading a string from Firebase and storing it as a CString
I have a mobile app (done using MIT App Inventor) storing some values to a Firebase database. App inventor stores all the values as strings (i.e. with quotes, and strings have quotes enclosed within ...