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.

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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:\\...
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12 votes
6 answers
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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'...
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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 ...
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2 answers
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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') { ...
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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); ...
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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 ...
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1 vote
2 answers
812 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 ...
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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 <...
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2 answers
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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 ...
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1 vote
0 answers
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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 ...
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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" ...
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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(...
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3 answers
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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, ...
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1 vote
1 answer
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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["...
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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....
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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 ...
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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 ...
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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 ...
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3 votes
2 answers
15k 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 ...
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7 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 ...
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1 answer
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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 ...
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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 ...
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2 answers
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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); ...
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1 answer
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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 ...
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13 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); ...
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