C++

Member_14611814

I am trying to learn c++ programming language and am still an amateur at it. I have a problem with "passing arrays in a function" and all am asking is what would be the easiest way to handle this problem?

Greg Utas

Here is a thread[^] that should answer your question, and then some.

Robust Services Core | Software Techniques for Lemmings | Articles

Lost User

Greg Utas wrote:

and then some

Should that be "and then lots"? ;)

CPallini

Be aware that the standard C++ library gently offers many alternative containers[^] to arrays.

charlieg

and are extremely useful, though sometimes performance is mystifying :)

Charlie Gilley <italic>Stuck in a dysfunctional matrix from which I must escape... "Where liberty dwells, there is my country." B. Franklin, 1783 “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759

CPallini

The right container for the right job...

charlieg

*sometimes*. And it may very well depend on the platform. I have a communications system that transmits data using tags and a parser. I have upwards of 500 data elements that can go back and forth. The initial implementation used a simple linear search for finding a passed tag. As time passed, the tag set became larger and larger. Hey, this is a good place for a mapped data set, allowing me to find the tag quickly I thought. The map turned out to be 3 times slower than the linear search. Never did figure out why. Showed the sample code to someone who loves the STL and has a lot more experience than I do. No idea. Someday I'll get back to it.

Charlie Gilley <italic>Stuck in a dysfunctional matrix from which I must escape... "Where liberty dwells, there is my country." B. Franklin, 1783 “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759

CPallini

My little experiment gives me opposite results:

#include #include using namespace std;

constexpr int Indices = 4096;
constexpr int Size = 512;

extern const int idx[Indices];
extern const string tag [Size];

int linear_search(const string & s )
{
for (int n = 0; n mtag;
for (int n=0; nsecond;
#endif
sum+=k;
}

cout << "sum " << sum << endl;
}

Where

tag is an array of 512 randomly generated strings (having length betwween 4 and 12)
idx is an array of 4096 randomly generated indices (for quickly gatering a candidate)

Output

g++ -D LINEAR_SEARCH -Wall lookup.cpp -o lookup_linear_search
g++ -Wall lookup.cpp -o lookup_map

time ./lookup_linear_search
sum 252632422

real 0m1,821s
user 0m1,811s
sys 0m0,008s

time ./lookup_map
sum 252632422

real 0m0,297s
user 0m0,297s
sys 0m0,000s

charlieg

Hmm, your code is surprising close to mine. What compiler are you using? I have to use VS2008 for embedded work, so maybe the STL implementation is suspect. I'll have to dust it off. Your results are what I would have expected.

Charlie Gilley <italic>Stuck in a dysfunctional matrix from which I must escape... "Where liberty dwells, there is my country." B. Franklin, 1783 “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759

CPallini

Quote:

What compiler are you using?

The good one. :laugh: The hint is in the command line[^]:

g++ -D LINEAR_SEARCH -Wall lookup.cpp -o lookup_linear_search

charlieg

:laugh:

Charlie Gilley <italic>Stuck in a dysfunctional matrix from which I must escape... "Where liberty dwells, there is my country." B. Franklin, 1783 “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759