You can either use a ternary, for simple cases: or, if it's more complicated, you might use a lambda that's called on-the-spot: Also, while not yet standard, statement expressions might help you: Thanks for contributing an answer to Stack Overflow! Learn more about Stack Overflow the company, and our products. You can simply use text_from_somewhere instead of msg. Looking at your code, instead of converting float to String in order to use String concatenation, then convert to an array, it will be much simpler to just directly create a char array with sprintf(). It is useful to the person writing the function, because if he screws up and tries to modify the argument, the compiler will throw an error. am i correct to think that this is what is happening with vw_send ? WiFi.begin (ssid, password); Share Improve this answer Follow answered Jun 21, 2017 at 20:00 Edgar Bonet | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | Because it's a very stripped down, simple example program. +---+---+---+---+---+---+---+---+ Find centralized, trusted content and collaborate around the technologies you use most. That is a recipe for stomping on random bytes of memory. IF you want to USE the pointer, you must make sure it points to valid, allocated memory. Asking for help, clarification, or responding to other answers. String concatenation isn't safe in Arduino which has only 2k memory and should avoid whenever is possible, especially if you are new to Arduino programming and not familiar with how dynamic memory allocation works internally. Arduino Stack Exchange is a question and answer site for developers of open-source hardware and software that is compatible with Arduino. Then create a new Thing, select/configure the device you want to use, and create the following variables: - automatic_mode - boolean - Read & Write. Does every Banach space admit a continuous (not necessarily equivalent) strictly convex norm? You pass in the float, how wide you want the whole number to be (if it will fit), the number of decimals of precision - and the buffer you want it to fill. But without seeing the rest of the code it's just a guess. Basically, I don't want it to print from a text directly. Hold that thought for a bit. Serial.print would print the entire string by doing something VERY similar of this: RayLivingston: Trying to understand const char usage - Arduino Forum (Ep. Otherwise, functions like Serial.print have no way of knowing WHERE the string ends, and will keep sending characters until it FINDS a '\0' somewhere in memory. You can simply use text_from_somewhere instead of msg. Compare const char * to const char - Arduino Stack Exchange Writing to either of those is bad Because vw_send does NOT take a char as its first argument, it takes a const char *. How much space did the 68000 registers take up? It only takes a minute to sign up. Would a room-sized coil used for inductive coupling and wireless energy transfer be feasible? The id field in the struct is not needed as the index is a function of the value (i.e. Haven't bothered to change the 1s and 0s This means that it is possible to do arithmetic on characters, in which the ASCII value of the character is used (e.g. I guess it's really just a matter of making vw_send use incomingByte. Again - thanks for explaining pointers so clearly and much more concise than the tutorials i've been reading. Below is my draft sketch. Character literals are written in single quotes, like this: 'A' (for multiple characters - strings - use double quotes: "ABC"). Advice for checking integrity of serial char strings? It is functionally equivalent to char * note = "Hi! Commercial operation certificate requirement outside air transportation. You may also, in some cases, need to do an explicit type cast, by preceding the variable name in the call to a function with the desired type enclosed in parens. Well, I've only been doing c programming for about 35 years, so, yeah, I'm pretty sure. I get this error: txVW.cpp: In function 'void loop ()': txVW:11: error: invalid conversion from 'char' to 'const char*'. Arrays are in consecutive memory addresses. | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | Address 6 - > contains ASCII code for 'o' 2 Answers Sorted by: 4 This begin () method expects a modifiable character array as its first argument. Powered by Discourse, best viewed with JavaScript enabled, invalid conversion from 'char' to 'const char'. Different maturities but same tenor to obtain the yield. Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? Mikael is also renaming your variables to more useful names another good idea : Could you post the code in full? I could understand your comment and solved following No.3! text_from_somewhere is ALREADY of type char *, the error is "invalid conversion from 'char' to 'char*' ", the error is "invalid conversion from 'char' to 'const char*' " (don't know how that came into the mix suddenly ). FWIW - here's the code from inside VirtualWire.cpp that i think is relevant; BabyGeezer: BabyGeezer: I've got a code which is going to read on SPIFFS file on my ESP32 and write it into the Serial monitor. from blind trial & error, i found that the following compiles okay; it seems rather ugly - is there a more elegant version ? convert String to type const char* using Arduino - Stack Overflow RayLivingston: RayLivingston: So, the fact that msg is declared const is totally irrelevent. @paolo Added the const. How to read ints from a txt file and save it to different consts in C? To convert a character to an integer you use this short statement: int a; char b; a=b-'0'; That's it! Is religious confession legally privileged? That's it. 1 Answer Sorted by: 24 There is a function in the standard Arduino library called dtostrf (). So there is NO valid conversion. It is the LOCAL name, to be used WITHIN the function to refer to that argument. Brute force open problems in graph theory, A sci-fi prison break movie where multiple people die while trying to break out, Using regression where the ultimate goal is classification. But I couldn't concatenate const char value to make new URL. The code I originally posted compiles, no problem. Accidentally put regular gas in Infiniti G37. It is a variable qualifier that modifies the behavior of the variable, making a variable "read-only". What languages give you access to the AST to modify during compilation? A c_string is simply a char array. Devices is an array with up to 8 entries 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, Temporary policy: Generative AI (e.g., ChatGPT) is banned, Testing native, sponsored banner ads on Stack Overflow (starting July 6), Read Extended ASCII Characters from File and Convert to ASCII Decimal Value, Read int and char from the same file in C, How cast char to int in C++? You can't come back and give it a different value now at runtime. When are complicated trig functions used? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Can you work in physics research with a data science degree? Using the code below, I want it to send out a variable's value instead of just "Hello". Thank you for your patience and the comprehensive reply, i will take the time to really let it sink in to understand usage of pointers, referencing and dereferencing, etc. Is there any potential negative effect of adding something to the PATH variable that is not yet installed on the system? That's it. means a malloc of 4 byte somewhere probably if the pointer life is "larger" than the "Hi!" How to convert char[] to int with fail\success control? and if i change the declaration of incomingByte, then; Your are creating a pointer to char, and setting it's value to zero, so it points to the first byte of memory. one's, something will fail. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. "; Note that you can't COPY the string into the address pointed to by 'note' since 'note' doesn't point to anything when it is created: that because "Hi!" Viewed 8k times. am i correct to understand that the part in bold means, "it can only read that argument" ? const - Arduino Reference Why did the Apple III have more heating problems than the Altair? index = id - '1'). Convert int to char [] I'm looking to convert an int value to a char array. which brings me back to confusion, as we had determined that 'const' (in the example) was irrelevant earlier ? What is the Modified Apollo option for a potential LEO transport? var: variable name. Creative Commons Attribution-Share Alike 3.0 License. Actually this can be improved further. Thanks for contributing an answer to Stack Overflow! Book or a story about a group of people who had become immortal, and traced it back to a wagon train they had all been on, Ok, I searched, what's this part on the inner part of the wing on a Cessna 152 - opposite of the thermometer. ========================== [FAILED] Took 3.48 seconds ==========================/ Arduino toCharArray () Append char String char void loop(){ String stringOne = "A long integer: "; stringOne += 1234; char charBuf[50]; stringOne.toCharArray(charBuf, 50) } C++ has a string object, but plain C used c_strings. Perhaps a diagram might help your understanding: msg: 16 bit/2 byte variable that contains an unsigned integer that corresponds to a physical address in the CPU's memory space, i.e. 587), The Overflow #185: The hardest part of software is requirements, Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood, deprecated conversion from string constant to 'char*'. Arduino error: invalid conversion from 'const char*' to 'char VALUE is a const char* the const part stands for "constant" in case that isn't obvious. Making statements based on opinion; back them up with references or personal experience. Miniseries involving virtual reality, warring secret societies. Step 2: Integer to Character This is more intricate than the last one. (Ep. Can the Secret Service arrest someone who uses an illegal drug inside of the White House? You then attempt to take the result of the Serial.read, and shove it into the pointer, so you now have a poitner that points to somewhere in memory, who knows where. Because vw_send does NOT take a char as its first argument, it takes a const char *. aarg: Do I have the right to limit a background check? Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. I have several const unsigned char in a .h file. char() - Arduino Reference Would a room-sized coil used for inductive coupling and wireless energy transfer be feasible? +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ convert a string to char for Arduino Ask Question Asked 1 year, 9 months ago Modified 1 year, 9 months ago Viewed 725 times -1 When I write String abc ="0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff"; const unsigned char displaydata []= {reinterpret_cast<const unsigned char*> (abc.c_str ())}; Is speaking the country's language fluently regarded favorably when applying for a Schengen visa? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Has a bill ever failed a house of Congress unanimously? You need a static char array and an index variable, to keep track of where to store the next character. Connect and share knowledge within a single location that is structured and easy to search. Allowed data types: any type. Converting an int or String to a char array on Arduino The Arduino programming language Reference, organized into Functions, Variable and Constant, and Structure keywords. That's it. I thought that the pointer will start on the nth slot, then go to the next based on the nth byte from serial? Sci-Fi Science: Ramifications of Photon-to-Axion Conversion. PROGMEM - Arduino Reference Not the answer you're looking for? It is a word document but I had to zip it so that it would be accepted as an attachment. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Accidentally put regular gas in Infiniti G37. In your code you've already assigned it the value "", an empty string. Relativistic time dilation and the biological process of aging. Does "critical chance" have any reason to exist? Can Visa, Mastercard credit/debit cards be used to receive online payments? (Here we are on the sample code given on many website). This is fine because it will allow you to deal with multiple chars ids. Arduino | Delft To declare a constant pointer it would be. The note variable is defined as a pointer, but it does not point to any space where characters can be stored. i certainly wouldn't dream of challenging the compiler at it's game ! thanks for your patience.. static char msg = str_out.c_str(); the function is declared like so; Don't get so hung up on the const, just accept that the compiler is right, since it pretty much always is. The "msg" in the argument list of a function does NOT refer to any specific variable. What you probably want to do is to interpret those incoming bytes as char s and accumulate those in a String. Can the Secret Service arrest someone who uses an illegal drug inside of the White House? Making statements based on opinion; back them up with references or personal experience. RayLivingston: Different maturities but same tenor to obtain the yield. how to change a const char* - Arduino Stack Exchange vw_send((uint8_t *)incomingByte, strlen(incomingByte)); This is exactly the same problem as the previous example BabyGeezer: it is a 'pointer' to another location in memory. Find centralized, trusted content and collaborate around the technologies you use most.
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