इस घटना में कि यदि कार्यक्षमता आपके सिस्टम के लिए महत्वपूर्ण है, तो वास्तव में पुरानी strstrपद्धति का उपयोग करना फायदेमंद है । std::searchभीतर की विधि algorithmसबसे धीमी संभव है। मेरा अनुमान है कि उन पुनरावृत्तियों को बनाने में बहुत समय लगेगा।
कोड है कि मैं समय के लिए इस्तेमाल किया पूरी बात है
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <random>
#include <chrono>
std::string randomString( size_t len );
int main(int argc, char* argv[])
{
using namespace std::chrono;
const size_t haystacksCount = 200000;
std::string haystacks[haystacksCount];
std::string needle = "hello";
bool sink = true;
high_resolution_clock::time_point start, end;
duration<double> timespan;
int sizes[10] = { 10, 20, 40, 80, 160, 320, 640, 1280, 5120, 10240 };
for(int s=0; s<10; ++s)
{
std::cout << std::endl << "Generating " << haystacksCount << " random haystacks of size " << sizes[s] << std::endl;
for(size_t i=0; i<haystacksCount; ++i)
{
haystacks[i] = randomString(sizes[s]);
}
std::cout << "Starting std::string.find approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(haystacks[i].find(needle) != std::string::npos)
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting strstr approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(strstr(haystacks[i].c_str(), needle.c_str()))
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
std::cout << "Starting std::search approach" << std::endl;
start = high_resolution_clock::now();
for(size_t i=0; i<haystacksCount; ++i)
{
if(std::search(haystacks[i].begin(), haystacks[i].end(), needle.begin(), needle.end()) != haystacks[i].end())
{
sink = !sink; // useless action
}
}
end = high_resolution_clock::now();
timespan = duration_cast<duration<double>>(end-start);
std::cout << "Processing of " << haystacksCount << " elements took " << timespan.count() << " seconds." << std::endl;
}
return 0;
}
std::string randomString( size_t len)
{
static const char charset[] = "abcdefghijklmnopqrstuvwxyz";
static const int charsetLen = sizeof(charset) - 1;
static std::default_random_engine rng(std::random_device{}());
static std::uniform_int_distribution<> dist(0, charsetLen);
auto randChar = [charset, &dist, &rng]() -> char
{
return charset[ dist(rng) ];
};
std::string result(len, 0);
std::generate_n(result.begin(), len, randChar);
return result;
}
यहाँ मैं यादृच्छिक उत्पन्न करता हूँ haystacksऔर उनमें खोज करता हूँ needle। हिस्टैक की गिनती निर्धारित है, लेकिन प्रत्येक हाइस्टैक के भीतर तार की लंबाई शुरुआत में 10 से बढ़कर अंत में 10240 हो जाती है। अधिकांश समय कार्यक्रम वास्तव में यादृच्छिक तार उत्पन्न करता है, लेकिन यह उम्मीद की जानी है।
आउटपुट है:
Generating 200000 random haystacks of size 10
Starting std::string.find approach
Processing of 200000 elements took 0.00358503 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0022727 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0346258 seconds.
Generating 200000 random haystacks of size 20
Starting std::string.find approach
Processing of 200000 elements took 0.00480959 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00236199 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0586416 seconds.
Generating 200000 random haystacks of size 40
Starting std::string.find approach
Processing of 200000 elements took 0.0082571 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00341435 seconds.
Starting std::search approach
Processing of 200000 elements took 0.0952996 seconds.
Generating 200000 random haystacks of size 80
Starting std::string.find approach
Processing of 200000 elements took 0.0148288 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00399263 seconds.
Starting std::search approach
Processing of 200000 elements took 0.175945 seconds.
Generating 200000 random haystacks of size 160
Starting std::string.find approach
Processing of 200000 elements took 0.0293496 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00504251 seconds.
Starting std::search approach
Processing of 200000 elements took 0.343452 seconds.
Generating 200000 random haystacks of size 320
Starting std::string.find approach
Processing of 200000 elements took 0.0522893 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00850485 seconds.
Starting std::search approach
Processing of 200000 elements took 0.64133 seconds.
Generating 200000 random haystacks of size 640
Starting std::string.find approach
Processing of 200000 elements took 0.102082 seconds.
Starting strstr approach
Processing of 200000 elements took 0.00925799 seconds.
Starting std::search approach
Processing of 200000 elements took 1.26321 seconds.
Generating 200000 random haystacks of size 1280
Starting std::string.find approach
Processing of 200000 elements took 0.208057 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0105039 seconds.
Starting std::search approach
Processing of 200000 elements took 2.57404 seconds.
Generating 200000 random haystacks of size 5120
Starting std::string.find approach
Processing of 200000 elements took 0.798496 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0137969 seconds.
Starting std::search approach
Processing of 200000 elements took 10.3573 seconds.
Generating 200000 random haystacks of size 10240
Starting std::string.find approach
Processing of 200000 elements took 1.58171 seconds.
Starting strstr approach
Processing of 200000 elements took 0.0143111 seconds.
Starting std::search approach
Processing of 200000 elements took 20.4163 seconds.