From: dyliu AT ms1 DOT hinet DOT net (Dong-Yueh Liu)
Newsgroups: comp.os.msdos.djgpp
Subject: Question about efficiency: vector vs. deque
Date: Wed, 20 Jan 1999 07:53:34 GMT
Organization: New Silkera Network
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I write a simple program to compare the efficiency of vector and 
deque. The code is like the following:

const int loop = 10000;
const int size = 2048;
vector<int> v1(size), v2(size);
deque<int> q1(size), q2(size);
time_t t1 = clock();
for (j = 0; j < loop; j++)
  copy(v1.begin(), v1.end(), v2.begin());
time_t t2 = clock();
for (j = 0; j < loop; j++)
  copy(q1.begin(), q1.end(), q2.begin());
time_t t2 = clock()

The program is compile with -O3 option to turns on optimizations.
The gcc version is 2.81. The run-time measured of the two loops 
in my PC are:
vector: 3.9011 seconds
deque: 3.2967 seconds

I am amazed by the result since I expected that vector should be
faster the deque, but the result is reverse. The following is that
I use VC++ 6.0 to compile the same program:
vector: 0.961 seconds
deque: 4.446 seconds

Can anyone explain why the efficiency of vector is worse than
deque using gcc2.81?