I'm working on a traveling sales person program in C++. I'm very new to C++ and its so much different from Java that the simple things really get confusing.
How do I use standard input to accept commands from a file (apparently I don't open the file, my professor just uses it to feed in commands or something) and then use those commands to run my program accordingly?
An example would be
city a
city b
city c
city d
a c 1300
a d 1400
a b 900
d c 1500
So basically an unknown amount of information is going to be passed into my program and then my program needs to declare a specific number of cities and then attach travel costs between each of them as specified. I think I can do the latter part, but my problem is knowing how to take an unknown number of inputs and then attach those inputs to variables.
I guess in Java I would do something like this:
While(nextLine = true){
if (nextLine.contains ("city"){
String nextLine = nextLine;
...and so on
}
}
Start with waiting a filename by ifstream, then you can get inputs by char or line in which using a char pointer and determine it with text size i believe somethig like this
std::ifstream::pos_type filesize(const char* filename)
{
Now you buffered, go on for what you know from java and combine it. Besides, like Sam's sugesstion, u you should read
Related
I have a static method that searches (and returns) into String msg the value between a TAG
this is the code function:
static String genericCutterMessage(String TAG, String msg){
Serial.print("a-----");
Serial.println(msg);
Serial.print("b-----");
Serial.println(TAG);
if(msg.indexOf(TAG) >= 0){
Serial.print("msg ");
Serial.println(msg);
int startTx = msg.indexOf(TAG)+3;
int endTx = msg.indexOf(TAG,startTx)-2;
Serial.print("startTx ");
Serial.println(startTx);
Serial.print("endTx ");
Serial.println(endTx);
String newMsg = msg.substring(startTx,endTx);
Serial.print("d-----");
Serial.println(newMsg);
Serial.println("END");
Serial.println(newMsg.length());
return newMsg;
} else {
Serial.println("d-----TAG NOT FOUND");
return "";
}
}
and this is output
a-----[HS][TS]5132[/TS][TO]5000[/TO][/HS]
b-----HS
msg [HS][TS]5132[/TS][TO]5000[/TO][/HS]
startTx 4
endTx 30
d-----
END
0
fake -_-'....go on! <-- print out of genericCutterMessage
in that case I want return the string between HS tag, so my expected output is
[TS]5132[/TS][TO]5000[/TO]
but I don't know why I receive a void string.
to understand how substring works I just followed tutorial on official Arduino site
http://www.arduino.cc/en/Tutorial/StringSubstring
I'm not an expert in C++ and Arduino but this looks like a flushing or buffering problem, isn't it?
Any idea?
Your code is correct, this should not happen. Which forces you to consider the unexpected ways that this could possibly fail. There is really only one candidate mishap I can think of, your Arduino is running out of RAM. It has very little, the Uno only has 2 kilobytes for example. It doesn't take a lot of string munching to fill that up.
This is not reported in a smooth way. All I can do is point you to the relevant company page. Quoting:
If you run out of SRAM, your program may fail in unexpected ways; it will appear to upload successfully, but not run, or run strangely. To check if this is happening, you can try commenting out or shortening the strings or other data structures in your sketch (without changing the code). If it then runs successfully, you're probably running out of SRAM. There are a few things you can do to address this problem:
If your sketch talks to a program running on a (desktop/laptop) computer, you can try shifting data or calculations to the computer, reducing the load on the Arduino.
If you have lookup tables or other large arrays, use the smallest data type necessary to store the values you need; for example, an int takes up two bytes, while a byte uses only one (but can store a smaller range of values).
If you don't need to modify the strings or data while your sketch is running, you can store them in flash (program) memory instead of SRAM; to do this, use the PROGMEM keyword.
That's not very helpful in your specific case, you'll have to look at the rest of the program for candidates. Or upgrade your hardware, StackExchange has a dedicated site for Arduino enthusiasts, surely the best place to get advice.
Referring to two questions:
Incorrect output from C++ Primer 1.4.4
Confused by control flow execution in C++ Primer example
My question is answered in both of those posts, but I want to delve further.
First, I know this is only the beginning, but let's say I make a fully functional program that runs in a designed window. By that level, will I already know how to implement a EOF? I can't expect someone running my program to know that they need to hit Control-Z.
Is there a way to implement a specific code that functions so that it does not need me to type in an unrecognized value?
Also one guy in those questions somewhat answered the importance of EOF, but how come the program doesn't even post the final cnt - 1?
Let's say I do the numbers 10 10 10 20 20 20. Without EOF, this will only show the "10 repeats 3 times." How come the program doesn't at least type in the count "10 repeats 3 times and 20 repeats 2 times" minus the final one with white space?
lets say I make a fully functional program that runs in a designed window. By that level, will I already know how to implement a eof? I can't expect someone running my program to know that they need to hit ctrl + z.
You could either tell the user explicitly to do a specific action to end input or the design of the window itself could tell the user the information implicitly. For instance, a dialog box could ask the user to enter input and click an OK button when done.
Is there a way to implement a specific code that functions so that it does not need me to type in an unrecognized value?
It seems like you would rather use a newline character to terminate your input. An example of this usage could be std::getline. Instead of writing
while (std::cin >> val)
you could instead use
std::string line;
if (std::getline(std::cin,line))
and assume that your user's input only consists of one line of values. There are plenty of other ways to similarly achieve this task depending on how you want to constrain the user's input.
Let's say I do the numbers 10 10 10 20 20 20. WIthout eof this will only show the "10 repeats 3 times." How come the program doesn't at least type in the count "10 repeats 3 times and 20 repeats 2 times" minus the final one with white space?
Without the eof your program is still executing the while (std::cin >> val) loop since std::cin >> val has not yet received invalid input.
Since the line
std::cout << currVal << " occurs " << cnt << " times" << std::endl;
occurs after that while loop finishes execution, you don't (yet) see any information about the three 20's in the input.
When you are reading a sequence of inputs you'll need some indication when your down. That could be a sentinel value ("enter 999 to stop reading"; you'd need to detect that while reading), an invalid input ("enter X to stop reading"; when reading an int the value X is illegal and causes the stream to got into failure mode, i.e., have std::ios_base::failbit set), or the more conventional "there isn't anything more to read". For a file, the last conditions is straight forward. When reading data from the console you'll either need to teach people how to terminate the input or you'll need to use a different approach.
If you want to intercept any keypressed and react on them directly you may do so, too. You could, e.g., use ncurses and control your input via that. You could also set the concole to non-buffering (on POSIX systems using tcgetattr() and tcsetattr() to clear the ICANON flag) and deal directly with all key presses to decide whether you want to continue reading or not.
Although I'm certainly up to doing fancy I/O stuff I normally don't bother: users will understand the "end of input" character and just deal with it. That is, my input normally looks something like this:
while (in >> whatever_needs_to_be_read) { ... }
... or, if the input is genuinely line oriented
for (std::string line; std::getline(in, line); ) { ... }
The function doing this input will then be called with a suitable std::istream which may be std::cin although I have typically some way to also read from a file (in addition to the shell-privided input redirection).
BTW, despite some indications in the questions referenced, "EOF" is not a character being read. It is a character entered, though (normally). ... and it is quite conventional to "know" the end of input character (on POSIX systems a ctrl-D and on Windows a ctrl-Z). You can use other indicators, e.g., the "interrupt" (ctrl-C) but that takes more work and doesn't integrate nicely with stream. To use the interrupt chacter you'd need to setup a signal handler for SIGINT and deal with that. One slightly annoying part of doing so is that if you get it wrong you'll need to find a different way to kill the program (e.g. on POSIX using ctrl-Z to put the process to sleep and kill it via a harsher signal).
lets say we have a cal.exe file (a simple addition calculator programmed programmed in c++).
lets say that the console output screen first displays enter the first number: and waits for the user to input an integer value. I am willing to create a c++ program that would "pass on" the required value to the running process (cal.exe) as an input (playing the role of a user). I would also like to have the output from the cal.exe file to be displayed and interpreted by my program.
I havent got the slightest idea how to proceed with this. Is there any open source library that would help me accomplish this? If there is, could you name a few?
I have just learned object oriented programming in c++ last year in my school and I am not used to these kind of stuff in programming; so please excuse me if this question is silly.
update:
lets consider 2 processes a.exe and b.exe running. could you tell me a possible way to program b.exe which provides a integer input to a.exe (a console process) as if it was from the user?
You can do this by accepting command line arguments.something like this
int main ( int argc, char *argv[] )
{
enter code here
return 0;
}
Where,
First argument to main function (argc) refers to the number of arguments being passed to the program at run-time.
Second (char *argv[] )refers to a string containing the arguments that are passed (char * is treated as String also ).
Argument names may vary as per the user specifications.
For details Refer:
http://www.cplusplus.com/articles/DEN36Up4/
And for nesting of programs you can use system("name of child program goes here") Function under stdlib.h.
For details Refer:
http://www.cplusplus.com/reference/cstdlib/system/
Actually I have trouble naming the title of this post. Because I don't know how to summarize my meaning in a professional way. But I'll explain my question as below:
I'm running a program written by C++, command is:
./VariationHunter_SC
Then it'll let you type in many parameters:
Please enter the minimum paired-end insert size:
Please enter the maximum paired-end insert size:
Please enter the pre-processing mapping prune probability:
Please enter the name of the input file:
Please enter the minimum support for a cluster:
Obviously I need to type in such parameters one by one to run the program; But I have thousands of such jobs, and need to pre-assign such parameters in script, and submit script to computer.
So how can I do that?
thx
Edit
so how can I make parameter-list?
Just like below?:
140
160
0
mrfast.vh
1
Seems the program cannot recognize these numbers, and distribute numbers..
This depends on how the program actually reads the data that you type in - it's likely that its reading stdin, so you could use separate files with the parameters and pass them in via redirection: ./VariationHunter_SC < parameter-file
It's also possible that the program will accept parameters on the command line, but there's no way of really knowing that (or how) except by whatever documentation the program might come with (or by reading the source code, if it's available and there is no other accurate docs).
Simply use the piping character to pipe the contents of a file to your program
example, in a windows command shell:
echo "asdf" | pause
This will pass "asdf" to the pause program. As a result, pause will print a "Press any key to continue" message, then imediately continue because it will receive the "asdf" string as a response.
So, overall, write or use a program that outputs the contents of your file. Call it, then pipe its output to the program that needs the input.
The unix cat command is such a command that writes the contents of a file to output, or to the input of another executable if you are piping the output.
I have a c++ program which performs one function. It loads a large data-file into an array, receives an array of integers and performs a lookup in that array, returning a single integer. I am currently calling the program with each integer as an argument, like so:
$ ./myprogram 1 2 3 4 5 6 7
I also have a ruby script, and I would like this script to utilize the c++ program.
Currently, I am doing this like so.
Ruby Code:
arguments = "1 2 3 4 5 6 7"
an_integer = %x{ ./myprogram #{arguemnts} }
puts "The program returned #{an_integer}" #=> The program returned 2283
This is all working properly, but my problem is that each time ruby makes this call, the c++ program has to reload the data-file (which is over 100mb) - very slow, and very inefficient.
How can I rewrite my c++ program load the file only once, allowing me to make many lookups via a ruby script without reloading the file each time. Would using sockets be a sensible approach? Writing the c++ program as a ruby extension?
Obviously I am not an experienced c++ programmer, so thanks for your help.
A possible approach is to modify your C++ program so that it takes its input from the standard input stream (std::cin) instead of from the command line parameters, and returns its result through the standard ouput (std::cout) instead of as main's return value. Your Ruby script would then use popen to launch the C++ program.
Assuming the C++ program currently looks like:
// *pseudo* code
int main(int argc, char* argv[])
{
large_data_file = expensive_operation();
std::vector<int> input = as_ints(argc, argv);
int result = make_the_computation(large_data_file, input);
return result;
}
It would be transformed into something like:
// *pseudo* code
int main(int argc, char* argv[])
{
large_data_file = expensive_operation();
std::string input_line;
// Read a line from standard input
while(std:::getline(std::cin, input_line)){
std::vector<int> input = tokenize_as_ints(input_line);
int result = make_the_computation(large_data_file, input);
//Write result on standard output
std::cout << result << std::endl;
}
return 0;
}
And the Ruby script would look like
io = IO.popen("./myprogram", "rw")
while i_have_stuff_to_compute
arguments = get_arguments()
# Write arguments on the program's input stream
IO.puts(arguments)
# Read reply from the program's output stream
result = IO.readline().to_i();
end
io.close()
Well,
You could go about this a number of different ways.
1) A simple, potentially ugly way to do this is to have your c++ run and intermittently check for a file, have your ruby script produce said file containing your arguments. Your C++ program would then use the contained arguments returning it's result to a result file which you could wait on within your ruby script... This is obviously HACK TASTIC but it's uber simple to implement and would work.
2) Expose your c++ code as a c extension to ruby. This is not as hard as it's sounds especially if you use RICE and would provide significantly less hackie solution.
3) If your c++ can be exposed through a c header file then it's almost trivial to construct a bridge using FFI. Jeremy Hinegardner gave a good lecture on constructing FFI interfaces at rubyconf heres the screencast
4) D-Bus provides an application communication bus, you could alter your C++ app to take advantage of said event bus and pass messages from your ruby using ruby-dbus
There are of course a thousand other routes... Maybe one or the other of these could prove viable :)
Cheers!