I am trying to learn c++, and for an assignment I have ran into a problem. I am trying to get an integer value from a string that a user enters all on one line.
Ex.) The user inputs: "Change value to 15."
What is the best way of getting the 15 from that string? I have looked around for a while, but could only find if a string was only integers.
Thanks in advance!
Why not use a mixture of getline(grabs your whole line) and string stream(tokenizes the input) and put them all in a vector(easier to use than an array), grab the one at .size()-1 and do an atoi on that. Might be overkill, but string stream could do what you want. For a small tut this could help http://www.dreamincode.net/forums/topic/95826-stringstream-tutorial/
This might not be the best way but to get something done now you can use strtok to tokenize your input string and then examine the tokens for your integer value integer. One of the answers here [link] suggests using strtok to tokenize a string.
If you know the format of you string or know that there will always be a single integer value then you can use string::find_first_of and string::find_last_of [link] and then just get the substring and use string::stoi.
Related
I am new to C++ and Arduino.
I have 3 variable of type char
char receivePayload[31];
char devID;
char switchState;
the data in receivePayload woudl be some like "01:01" or "01:00". Here the first part before colon is device ID and second part is switchState.
Can you please help me and explain how I can split the 2. I did read about strtok but was unable to understand.
The desired output would be like
devID would have 01 stored and
switchState would have 01 or 00 stored.
Also if I can convert it into integer.
Thanks a ton.
As for your problem, there are multiple solutions to it: One is using std::getline as tokenizer. Another is using std::string::find and std::string::substr. Yet another solution is to use the old C function strtok.
The above solutions all give you strings, so either you have to make devId and switchState strings as well, or use e.g. std::stoi to convert the strings to integers.
Apparently the Arduino platform have neither of the functionality listed above, which mean you have to tokenize the string yourself. This is, however, very simple: Find the separator (the ':' character), copy from the beginning to (but not including) the separator into a temporary string and convert it to an integer with e.g. std::strtol. Then copy from (but not including) the separator into the temporary string and convert that value to an integer.
If you don't even have std::strtol then use std::atoi.
Since this is Arduino, you should probably use the String class since it handles a lot of the annoying stuff for you like conversion to int without having to explicitly link against glibc.
You could split the string like so:
String receivedPayload("01:10");
String devId = receivedPayload.substring(0, receivedPayload.indexOf(':'));
String switchState = receivedPayload.substring(receivedPayload.indexOf(':'));
Converting them into an integer would involve just using toInt on the string objects.
If you didn't need to convert into an integer, it would have been easier to tokenise the string yourself by using a for loop and checking if the character is equal to ':' since the string is so short.
I have a binary string like "01001111111". I want to know that if that string contains "0" or not. How to do that ? And if I want to convert it into integer, how to get that ?
Since this seems to be a homework, so giving complete solution would not be a nice idea.
However, I would give you this hint:
std::bitset
std::string and related functions from <algorithm> header.
These two together should solve your problem if you learn to use them cleverly.
I have a c++ program, I would like the first argument of the main (argv[1]) to correspond to a table of float. Is it possible to do that??
I was thinking about putting in a string my floats separated with spaces (e.g. "1.12 3.23 4.32 1.1 ...")
Is there a way to automatically convert such a string into a table of floats? If I understand well the atof function converts a string into a double. So it seems it could be possible to split my string using the spaces and then convert each portion using atof.
This option does not seem to be very efficient to me? In addition it returns double and not float :(
So, is there a better way to pass table of float as argument of a c++ program ?
Thank you
A stringstream can do both the splitting at spaces and the parsing into a float.
std::stringstream ss(the_string);
std::vector<float> v(std::istream_iterator<float>(ss),
(std::istream_iterator<float>()));
// the extra parentheses here are ugly but necessary :(
How to obtain the string with the data depends on how large it is and where it is supposed to come from. Just keep in mind that in many systems the arguments passed to program are already split by spaces, putting each part in a different element of argv.
Save it in a text file, and then read it from the file when your program starts. I isn't worth it to pass it as a command-line argument.
The main() parameter list is as it is. You can pass the strings of your numbers as arguments to your program. The main function will have to parse its argument.
When you want to pass a space separated list of numbers in argv[1] you can use the strtok function to get the individual number strings and have to pass it to a conversion function.
When your conversion function returns a double you should check that the result can be represented by a float and cast the value to a float variable. But I would consider to use double as the internal representation.
In addition to Singer's answer:
The commandline should be used mainly by human, not computer. If you really need a table of values, use configuration file. You can always use human readable format for it.
I'm constructing a line command based chess engine. When a command is given to the engine (as a string), I have a couple of regex expressions run to determine if the command is valid. If it's valid, then the command is passed on to be parsed.
When a command such as a6a4 is given to the engine in string input;, is it valid to use a command like:
istringstream (input.at(1)) >> originalx; or:
istringstream buffer(input.at(1)); buffer >> originalx;
to convert just the part of the string with the integer into an actual int? I have been trying these methods of conversion, all using str.at(x) rather than just str and none of them seem to be working.
I know this may seem like a duplicate question because everyone wants to know how to convert an entire string to an int, but what about just a specific part of a string? I did search Google for answers as well but nothing I found was helpful.
I know this may seem like a duplicate question because everyone wants to know how to convert an entire string to an int, but what about just a specific part of a string?
A specific part of a string is still a string. You can just do str.substr(1, 1) and convert that whole sub-string to an int.
I am getting command line argument when i launch the application.
I am getting four parameter from command line.
after parsing I store them in four std::string/CString(mfc) variable now i need to know whether the value is decimal or not.because these parameter is going to be used in some mathematical calculation.
Can anybody help me on this.
here you can find how to determine if a string is a numeric, in 70 languages!
I'm not sure if all the solutions check the same thing. The C++ implementation checks if the input is a positive/negative integer/floating-point for base 10, or if it a is positive/negative integer for base 8/16. Is that what you want? Do you need to support only positive numbers? Do you need to support floating-points?
Probably you'll need to convert your input strings to numeric value, so there is no reason to do it in two steps (to check, then to convert). Better do it in a single step.
One more thing: If the input string is too long, for example "32525252332912461984612491264912649126129319312931279171295127951275129" - you normally won't want to consider it as a valid input.
Look at every character in the string, and if you find something that is not a digit, or a '.', then it is not a number.
Just use a string->number conversion function that unambiguously reports failure.
e.g. strtod and not atof