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On February 01 2013 04:47 omarsito wrote:Show nested quote +On February 01 2013 04:29 tec27 wrote:On February 01 2013 04:03 omarsito wrote:Sup ya'll, im currently busy with a C function thats supposed to copy a matrix to another matrix at another memory adress. So I coded my function and tested it, with both matrix having the same sizes. And right now the code copies fine until the last two values where it just doesnt want to copy them.
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
I'd be very happy if someone could help me out, im also open for feedback to changes for the function that doesnt involve memcopy! This looks fine to me, but is there any particular reason you're doing the pointer math instead of just using them like the arrays they are? e.g.: void matrixcopy(int** dest, int** src, int row_count, int col_count) {
int row, col;
for(row = 0; row < row_count; row++) {
for(col = 0; col < col_count; col++) {
dest[row][col] = src[row][col];
}
}
} No particular reason only other then that it felt easier from the beginning. I tried using your solution but I get a segmentation fault when it tries to call the function. Could it be because i call the function with the call matrixcopy(rmat, imat, ROWCOUNT, COLUMNCOUNT); where rmat is the destination matrix and imat source matrix
The segfault could be because you are using rmat and imat as a solid string of data, and the matrixcopy is expecting the first ROWCOUNT values as addresses to each row of data. Matrix copy is literally expecting an array of arrays, where your first implementation is a straight copy of data, where the amount of data is ROWCOUNT*COLUMNCOUNT.
hmmm, perhaps thats the problem anyhow... Maybe you need to account for the size of the pointers in the array in your first function to fix your off-by-two-error. What is the value of ROWCOUNT and COLUMNCOUNT?
yawn, here's another version (that assumes sizeof(int) and sizeof(int*) are the same, don't take this as true for all systems)...
void matrixcopy(int* dest, int* src, int row_count, int col_count) {
int length = sizeof(int *) * row_count + sizeof(int) * row_count * col_count; //calculate the number of bytes the transfer
int* end_ptr = dest+length/sizeof(int);
while( dest < end_ptr) { //stop copying when you reach the end
*dest = *src;
dest++; //increments destination pointer by sizeof(int)
src++;
}
}
It's no better than your version, just my own take on the function. In fact, this is worse than the second version for a multitude of reasons. At least we can be sure the memory is contiguous 
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On February 01 2013 04:03 omarsito wrote:Sup ya'll, im currently busy with a C function thats supposed to copy a matrix to another matrix at another memory adress. So I coded my function and tested it, with both matrix having the same sizes. And right now the code copies fine until the last two values where it just doesnt want to copy them.
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
I'd be very happy if someone could help me out, im also open for feedback to changes for the function that doesnt involve memcopy!
Your function looks fine, it could be that there is an error from the usage of it (perhaps it was called with erroneous row/column parameters?).
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On February 01 2013 05:04 RoyGBiv_13 wrote:Show nested quote +On February 01 2013 04:03 omarsito wrote:Sup ya'll, im currently busy with a C function thats supposed to copy a matrix to another matrix at another memory adress. So I coded my function and tested it, with both matrix having the same sizes. And right now the code copies fine until the last two values where it just doesnt want to copy them.
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
I'd be very happy if someone could help me out, im also open for feedback to changes for the function that doesnt involve memcopy! Fascinating... the last *two* values? Is that an entire row, or is just the last two values in the row? Can you share where you are malloc'ing for these data? I've never gotten that pointer assignment to every work in my own experience, for some reason or another, and I always end up using memcpy. If you want to optimize this a bit, you can use an intermediary 64-bit register if you are running this on your x86-64 pc. The compiler will probably optimize this anyway by unrolling the loop and using a register, but maybe not (you can check the assembly if you're crazy).
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
register long temp;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = (temp = *(srcmat+rowcount*i+j));
}
Uh, im not using malloc if you meant that.
Also for your question, its the last two values, aka [2][2] and [2][3].
Here's the printed data from printf
+ Show Spoiler +
Examining imat:
memory at: 404100 contains value: 10000
memory at: 404104 contains value: 10001
memory at: 404108 contains value: 10002
memory at: 40410c contains value: 10003
memory at: 404110 contains value: 10100
memory at: 404114 contains value: 10101
memory at: 404118 contains value: 10102
memory at: 40411c contains value: 10103
memory at: 404120 contains value: 10200
memory at: 404124 contains value: 10201
memory at: 404128 contains value: 10202
memory at: 40412c contains value: 10203
Examining rmat:
memory at: 404140 contains value: 10000
memory at: 404144 contains value: 10001
memory at: 404148 contains value: 10002
memory at: 40414c contains value: 10003
memory at: 404150 contains value: 10100
memory at: 404154 contains value: 10101
memory at: 404158 contains value: 10102
memory at: 40415c contains value: 10103
memory at: 404160 contains value: 10200
memory at: 404164 contains value: 10201
memory at: 404168 contains value: 0
memory at: 40416c contains value: 0
Also i'll post the whole code while we're at it, its short so i hope it helps(it contains some code that isn used atm because its my homework for c)
+ Show Spoiler +
#include <stdio.h>
#define ROWCOUNT (3)
#define COLUMNCOUNT (4)
int imat[ ROWCOUNT ][ COLUMNCOUNT ];
char cmat[ ROWCOUNT ][ COLUMNCOUNT ];
double dmat[ ROWCOUNT ][ COLUMNCOUNT ];
int rmat[ ROWCOUNT ][ COLUMNCOUNT ];
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
int main()
{
int i; int j;
int * ip; char * cp; double * dp;
for( i = 0; i < ROWCOUNT; i = i + 1 )
for( j = 0; j < COLUMNCOUNT; j = j + 1 )
{
imat[ i ][ j ] = 10000 + 100*i + j;
cmat[ i ][ j ] = 10*i + j;
dmat[ i ][ j ] = 1.0 + i/100.0 + j/10000.0;
rmat[ i ][ j ] = 0;
};
printf( "\n Examining imat:\n" );
for( ip = &imat[ 0 ][ 0 ];
ip <= &imat[ ROWCOUNT - 1 ][ COLUMNCOUNT - 1 ];
ip = ip + 1 )
printf( "memory at: %lx contains value: %d\n", (unsigned long) ip, *ip );
printf( "\n Examining cmat:\n" );
for( cp = &cmat[ 0 ][ 0 ];
cp <= &cmat[ ROWCOUNT - 1 ][ COLUMNCOUNT - 1 ];
cp = cp + 1 )
printf( "memory at: %lx contains value: %d\n", (unsigned long) cp, *cp );
printf( "\n Examining dmat:\n" );
for( dp = &dmat[ 0 ][ 0 ];
dp <= &dmat[ ROWCOUNT - 1 ][ COLUMNCOUNT - 1 ];
dp = dp + 1 )
printf( "memory at: %lx contains value: %f\n", (unsigned long) dp, *dp );
/* Add a statement here to call your matriscopy function. */
matriscopy(rmat, imat, ROWCOUNT, COLUMNCOUNT);
printf( "\n Examining rmat:\n" );
for( ip = &rmat[ 0 ][ 0 ];
ip <= &rmat[ ROWCOUNT - 1 ][ COLUMNCOUNT - 1 ];
ip = ip + 1 )
printf( "memory at: %lx contains value: %d\n", (unsigned long) ip, *ip );
return( 0 );
}
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Your code (as posted above) is pretty nice to read but please, for the love of all that is good, don't make redundant comments... if you can read the code and it is eminently clear what the code does (like incrementing a column in a for loop or "calling your function") then please don't put comments!
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Most of that code is built on their standard code, including all the comments. It's like a two week period where we're supposed to learn C from scratch which then will be used for some hardware so the teachers kinda have to point out exactly where everything is supposed to go
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Yeah and in my humble opinion, teachers usually instill some really bad habits when it comes to commenting and such
It was exactly the same when I learnt C/matlab etc... they'd tell you to put comments everywhere but once you can actually write little programs that work (like yours), you realise that the comments just get in the way and are kind of a psychological stumbling block to debugging programs.
I now try to reserve comments for tricky functions and confusing sections of code... and it's made quite a difference to readability! :D
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On February 01 2013 05:28 ThatGuy wrote:Show nested quote +On February 01 2013 04:03 omarsito wrote:Sup ya'll, im currently busy with a C function thats supposed to copy a matrix to another matrix at another memory adress. So I coded my function and tested it, with both matrix having the same sizes. And right now the code copies fine until the last two values where it just doesnt want to copy them.
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
I'd be very happy if someone could help me out, im also open for feedback to changes for the function that doesnt involve memcopy! Your function looks fine, it could be that there is an error from the usage of it (perhaps it was called with erroneous row/column parameters?).
The error is here: *(destmat+rowcount*i+j) = (temp = *(srcmat+rowcount*i+j));
Use columncount, not rowcount. The stride is off by 1 for each iteration of row.
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On January 30 2013 05:40 LukeNukeEm wrote:Hi, im playing around with the Code Analysis tool provided by Visual Studio and noticed the following: //Foo.h
class Foo
{
public:
int& operator [] (unsigned int i);
private:
int x[3];
}; //Foo.cpp
#include "Foo.h"
int& Foo::operator [] (unsigned int i)
{
return x[i];
} //main.cpp
#include "Foo.h"
int main(void)
{
int x[3];
x[5]; // this gets detected
Foo foo;
foo[5]; // this does not
int *y = new int; // neither does this (no delete)
} Are there any settings i can change to enable the code analysis tool to identify these errors?
"foo[5]" is not an error as the operator is overloaded. You aren't required to do anything with the value returned, so the analysis tool assumes that you're doing something valid.
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On February 01 2013 06:16 Phunkapotamus wrote:Show nested quote +On February 01 2013 05:28 ThatGuy wrote:On February 01 2013 04:03 omarsito wrote:Sup ya'll, im currently busy with a C function thats supposed to copy a matrix to another matrix at another memory adress. So I coded my function and tested it, with both matrix having the same sizes. And right now the code copies fine until the last two values where it just doesnt want to copy them.
void matriscopy (int * destmat, int * srcmat, int rowcount, int columncount)
{
int i, j;
for (i=0; i<rowcount; i=i+1) /* rad-nr */
for (j=0; j<columncount; j=j+1) /* kolumn-nr */
*(destmat+rowcount*i+j) = *(srcmat+rowcount*i+j);
}
I'd be very happy if someone could help me out, im also open for feedback to changes for the function that doesnt involve memcopy! Your function looks fine, it could be that there is an error from the usage of it (perhaps it was called with erroneous row/column parameters?). The error is here: *(destmat+rowcount*i+j) = (temp = *(srcmat+rowcount*i+j)); Use columncount, not rowcount. The stride is off by 1 for each iteration of row.
Thanks, that helped!
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On February 01 2013 06:28 Phunkapotamus wrote:Show nested quote +On January 30 2013 05:40 LukeNukeEm wrote:Hi, im playing around with the Code Analysis tool provided by Visual Studio and noticed the following: //Foo.h
class Foo
{
public:
int& operator [] (unsigned int i);
private:
int x[3];
}; //Foo.cpp
#include "Foo.h"
int& Foo::operator [] (unsigned int i)
{
return x[i];
} //main.cpp
#include "Foo.h"
int main(void)
{
int x[3];
x[5]; // this gets detected
Foo foo;
foo[5]; // this does not
int *y = new int; // neither does this (no delete)
} Are there any settings i can change to enable the code analysis tool to identify these errors? "foo[5]" is not an error as the operator is overloaded. You aren't required to do anything with the value returned, so the analysis tool assumes that you're doing something valid.
He's talking about out of bounds array indices.
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any Germans here?
I'm looking to brush up on my German and practice some EECS while I'm at it.
So, I'm looking for good intro German texts on circuits, C, AI, and machine structure;
stuff like
Ulaby & Maharbiz, Circuit, 2nd edition
Patterson + Hennessey
Kernighan + Ritchie
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Anybody here know anything about Windows 8/Windows Phone development? I have no idea even what language it is, though I suspect it's probably Java. Any good book recommendations? Or web sites that would give a crash course on it? Thanks!
Edit: Ok, I managed to find that you can compile apps on the Windows Phone using C++, C#.NET, and VB.NET. I still need some kind of introduction of some sort. Any advice on how to get started would be greatly appreciated.
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You can get translated copies of P&H for like $30 on amazon. If you don't know technical German it might be a bit daunting though... very different from conversational stuff.
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On February 01 2013 07:55 wherebugsgo wrote:
any Germans here?
I'm looking to brush up on my German and practice some EECS while I'm at it.
So, I'm looking for good intro German texts on circuits, C, AI, and machine structure;
stuff like
Ulaby & Maharbiz, Circuit, 2nd edition
Patterson + Hennessey
Kernighan + Ritchie
Especially K&R should have a translated version. At least... it would surprise me if it didn't.
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On February 01 2013 17:10 phar wrote:
You can get translated copies of P&H for like $30 on amazon. If you don't know technical German it might be a bit daunting though... very different from conversational stuff.
Half of a German computer science book is English words anyway. Or just German versions of the exact same English word.
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Canada2068 Posts
I saw this website advertising a C++ Grandmaster Certificate. Is it a good way of getting hired for your first job/learning the programming language in lieu of formal education i.e. university/college? It says it's free, so that's why I think it looks promising.
http://www.cppgm.org/index.html
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On February 01 2013 07:55 wherebugsgo wrote:
any Germans here?
I'm looking to brush up on my German and practice some EECS while I'm at it.
So, I'm looking for good intro German texts on circuits, C, AI, and machine structure;
stuff like
Ulaby & Maharbiz, Circuit, 2nd edition
Patterson + Hennessey
Kernighan + Ritchie
you should use lisp for AI, not C!
i don't know if you should, but i wanted to make a pun
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On February 01 2013 21:03 CountChocula wrote:I saw this website advertising a C++ Grandmaster Certificate. Is it a good way of getting hired for your first job/learning the programming language in lieu of formal education i.e. university/college? It says it's free, so that's why I think it looks promising. http://www.cppgm.org/index.html
Yeah, if you write a fully C++11 compliant compiler, it'll get you hired in lots of places if you show it to people who know what they're talking about. Problem is, that course is a pretty elegant way to spent hundreds (more likely thousands) of hours with. I'd be very surprised if anyone in that course reaches the project goal.
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On February 01 2013 21:03 CountChocula wrote:I saw this website advertising a C++ Grandmaster Certificate. Is it a good way of getting hired for your first job/learning the programming language in lieu of formal education i.e. university/college? It says it's free, so that's why I think it looks promising. http://www.cppgm.org/index.html
No that course is not good for you. It is a course for serious professionals who want to know how to write compilers, which for 99% of software engineers isn't necessary information, you need a basic understanding of what's going on for sure but you don't need to have written your own compiler.
If you have zero experience you aren't going to complete that course in any kind of realistic time frame. Go check out places like EdX and Coursera for good, undergrad level courses to give you a better idea of what you need to know, they are also free.
As a side note though, don't expect to get a job doing C++ without a degree. It's not going to happen. Sure someone will point to an exception, but that person wouldn't have been asking that kind of question, they would've got a job because they already had more experience than a graduate doing their own projects (ie 3+ years of serious stuff).
Go to university, or do it as a hobby.
EDIT:
Just a little snippet from that courses FAQ that you might want to take to heart:
This is a "Grandmaster" level programming course for world-class senior software engineers. It will be very difficult and mind-bending work.
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On February 01 2013 12:30 enigmaticcam wrote:
Anybody here know anything about Windows 8/Windows Phone development? I have no idea even what language it is, though I suspect it's probably Java. Any good book recommendations? Or web sites that would give a crash course on it? Thanks!
Edit: Ok, I managed to find that you can compile apps on the Windows Phone using C++, C#.NET, and VB.NET. I still need some kind of introduction of some sort. Any advice on how to get started would be greatly appreciated.
MSDN is the place to go.
http://msdn.microsoft.com/en-us/library/windows/apps/br211386.aspx
You can do HTML 5 ( HTML5, CSS3+JS), C# or C++.
If you have no experience, don't go with C++.
C# has a tonne of a material around about it, you'll probably find an answer to any question you have but using HTML5 is probably your safest option.
Mind if I ask what your goal is? It would give us a better idea of what tools you will need.
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EPT
