C++ :: Getting Unexpected Outputs For Bitfields And Floats
Aug 7, 2013
I'm getting unexpected output in 2 different cases. The 1st deals with bitfields. The C++ standard has this line about integral promotions:
An rvalue for an integral bit-field (9.6) can be converted to an rvalue of type int if int can represent all the values of the
bit-field; otherwise, it can be converted to unsigned int if unsigned int can represent all the values of the bit-field.
If the bit-field is larger yet, no integral promotion applies to it. If the bit-field has an enumerated type, it is treated as any other value of that type for promotion purposes.
This sounds like the value of a bitfield will always be treated as a signed int if the signed representation of the value will fit in the bits. This seems to hold true for my C compiler, but not my C++ compiler.
I tried storing a small negative value in a bitfield that has enough bits to store the sign bit and the value. But when I print out the bitfield, I always get a large number
The other issue I'm having is sort of similar. I'm trying to store 4294967295 into a float, but when I print it out, I get 4294967296. i've tried storing a few other large values like this and what's printed out is rarely the value I stored. I thought it might be because of some int to float conversion, so I tried 4294967295.0. Still no luck. Then I remember that defaults to a double so maybe that's the issue so I tried 4294967295.0f. Still no luck. Why can't I store the correct value here? I don't think it's an IEE format thing since I can use these values as floats on a calculator program.
The example code showing both issues is below.
Code:
#include <stdio.h>
typedef struct {
signed char x : 5;
signed char y : 3;
}my_struct_t;
I am having a hard time with some of my homework, specifically regarding how to printf floats. I can't seem to print the number i want out using float, it just becomes a jumbled mess.
Thats the code I currently have, I've probably tried everything to get the number to come out, but I just cant seem to figure it out. It should look like this, but with different numbers and stock:
I am new with C programming and trying to learn how to create functions such as floats. But for some reason when I try to compile this program the compiler will tell me Weight() is not a function.
I'm trying to compare two float ranges and it seems to be a hit and miss. I'm trying to use a object origin and dimensions comparing it to another set for collisions.
Say I have a std::vector of size 10 of float. This will be a windowing average, as each cycle I need to remove the oldest element and add a new element. I figured vector was good because I can pop_front() then push_back(). Is there any clever way to get the average of the vector without using a for loop?
I made this dice simulator which basically throws the dice 1 million times and outputs the frequency and percentage average for each side (1 to 6).
Everything is working fine, except my averages (floats) seem to be rounding up, causing 4% being "unassigned" at the end of the million rolls. I'm outputting with a setprecision of 2, but I only get 0's and no fractional numbers.
Im using the remquo function in the cmath library as follows:
int quotient; double a = remquo (10.3, 4.5, "ient);
This gives the correct remainder (a = 1.3) and quotient (quotient = 2).
Infact about 50% of the answers are right when I play around, however, trying something like:
int quotient; double a = remquo (2.25, 1.5, "ient);
yields an incorrect quotient of 2 and remainder of 0.
I do think this has something to do with float arithmetic. I recall tinkering with the float number 0.500 and that the CPU actually saves it as 0.50000000000000231. However if my suspicion of float arithmetic as the suspect is correct, I do not understand why a tenth decimal would make such a drastic difference as changing the quotient result.
I am currently trying to understand why this example for using an array as an argument in a function has a different result than what the lecture notes say it should be.
So supposedly sum should return with the value 28, but I get 27 no matter what. I also am not very good at reading and understanding what exactly the order of operations for this function are.
Code: #include <iostream> using namespace std;
int sum(const int array[], const int length) { long sum = 0; for (int i = 0; i < length; sum += array[++i]); return sum;
I am working through Binary IO with objects and am running into a curious error.
The program executes perfectly until it hits the very end. At "return 0", the program fails. The debugger picks up SIGABRT when executing "return 0". This seems to me to indicate a deconstructor problem of some kind. However, I can't seem to find any deconstructor problems (I am fairly new at programming though).
then the program finishes exiting without error . . . . but the whole point is to be able to read from the binary file. With those two lines in the code, the program successfully reads from the file and outputs the objects to the console ,but fails at "return 0";
Here is the code:
#include <iostream> #include <fstream> #include "Student.h" using namespace std;
My compiler (GCC) keeps expecting an expression where it shouldn't in 1 specific piece of my code:
int zxcNewWindow( HWND parent, TCHAR *text, zxWINDOW *kid, UINT style, int x, int y, int w, int h, int type ) // right here { *kid = zxDefWINDOW;
The project contains only 2 files right now and the settings are just the default for an empty Code::Blocks 12.11 project. Both files are in UTF-8 format (tried in ASCII too), I just cannot see why this is not compiling correctly. I'll post the files in the next two posts.
Edit: For those of you who didn't get what the error was from the above here's the full log:
mingw32-gcc.exe -Wall -g -DzxDEBUG -c C:MePrjscppzxGUImain.c -o objmain.o C:MePrjscppzxGUImain.c: In function 'zxcNewWindow': C:MePrjscppzxGUImain.c:39:10: error: expected expression before '{' token Process terminated with status 1 (0 minutes, 0 seconds) 1 errors, 0 warnings (0 minutes, 0 seconds)
I'm just starting c++, doing tutorials. So many tutorials. I've noticed that the tutorials all assume the same thing: That the user will always do exactly as he/she is told when asked for input.
Example: "Please enter your age:"
Now, the example code might be expecting the user to type some numbers, but what if the user feels like typing out the letters of their age?
"I am ninety five thank you very much, sonny"
I could specify to the user that I only want the information in number form, but what if the user is just being a dick?
What if the user types, "none o' yer business."?
So... how to approach "fool-proofing" player input?
I keep getting a segmentation error when ever I have the following code...
int main(void) { //Section 1 unsigned long val = 12; std::vector<unsigned long> vval; for(unsigned long i = 0; i < 100; ++i) { vval.push_back((unsigned long)0);
I have a WordRecord that contains a LinkedList (both my doing). I have rigorously tested my LinkedList class, and know that it works (heck, I used it in the last project I had!). The problem is that undefined behaviour seems to happen when using the WordRecord, which has a std::string and a LinkedList<unsigned>. (The problem happens with the LinkedList.)
Here is the code:
main.cpp #include <iostream> #include "BinaryTreeNode.h" // here for test purposes #include "LexicographicTree.h" #include "LinkedList.h"//also for test purposes #include "OutputStream.h" #include "WordRecord.h" using namespace std; int main() { // setup the OutputStream to print to "test.txt" OutputStream stream("test.txt"); // create a sampleWordRecord (make it have the word "I" on line 1)
[code]....
One of the requirements for the project is that it must compile on Unix server (I am using Windows, and have tested it in both environments.) I get a core-dump in the Unix environment. On the other hand, the output on-screen in the Windows environment looks right. However, when I open up the text file, I get the following
Sample word record:
WordLines I{14} /* I have no what is happening to sampleWordRecord's LinkedList; I am not trying to modify it, except for where I created the sampleWordRecord! */
So the latest challenge from jumping into c++ is as following.
Code: Write a function that builds the multiplication table of arbitrary dimensions This chapter also talks a ton about 2d arrays.
So I've built my program thus far as this.
Code: #include <iostream> using namespace std; int drawTable(int,int); int main()
[Code] .....
So basically, the idea is that I can use the arrays dimensions as a placeholder, and just multiple them to get that specific spot, so table[0][0] = 0, [0][1] = 0 and so on. However the output actually seems to be randomly generated numbers so I'd like to ask, what am I doing wrong? Am I on the right track? Or have I missed the bus stop completely.
I predicted the outcome as being 01230 as I thought the prefix decrement operator on iterator ce would prevent the final element of the list from being transformed.
I was wrong, the correct output is 01234.
So, I removed the decrement prefix and ran the test again, expecting a different result. It wasn't! The result was still 01234.
Only when I decremented ce twice did I get the result I initially expected, 01230.
why the first decrement of ce appears to have no effect?
My Windows service may download a binary update in the background using WinHTTP APIs. I'm using code similar to the one from the bottom of this MSDN page. For ease of access I'll copy if below:
The issue I'm experiencing is that while downloading, the code above "hogs" most of the bandwidth available on the client computer. My goal is to make it "throttle" itself on a configurable "bps" level, say at 50 kbps and not use any more bandwidth.
Someone suggested measuring my current download speed (in bps) and depending on the value make the thread "sleep" before calling WinHttpReadData again.
Code: DWORD DesiredBitsPerSec = 50 * 1000;//for 50 kbps if(fBps > DesiredBitsPerSec) { DWORD dwW = (DWORD)((fBps - DesiredBitsPerSec) * 1000) / DesiredBitsPerSec; if(dwW > 0) ::Sleep(dwW);//Sleep to throttle the download speed to the one we need }
So I implemented it into the code above but it didn't work -- the Sleep API would produce very strange delays. So I decided to add a little bit more tracking code to actually be able to see what BPS values I'm getting.
I created a small test project that is attached to this post to illustrate the issue. (It's hard to explain without running an example.)
For a test I began downloading a large binary file (Windows 10 MSI, off Microsoft's server) and at the same time had the Task Manager open on a Performance tab that was showing me the current network throughput. I made a screenshot:
But as you can see, the reading on the test program and the actual network BPS values differ greatly.
