使用profile来得到程序运行信息
profile程序可以用来监测程序不同部分（主要是各个函数）的使用时间和调用次数。
因此可以使用这个程序来鉴别程序中那个函数是整个程序的瓶颈，从而可以通过优化这个
函数来提高程序的性能。
Unix/Linux系统提供了GPROF这个profile程序。该程序提供两种信息：
1、程序中每个函数的CPU使用时间。
2、每个函数的调用次数。并提供简单调用关系图。
使用GPROF步骤如下：
1、用gcc或g++编译程序时，使用-pg参数，如：g++ -pg -o test.out test.cpp
2、执行编译得到的运行程序。如：./test.out
该步骤运行程序的时间会稍慢于正常编译出来的程序执行时间。而且会产生一个
gmon.out文件。
3、使用gprof命令。如：gprof test.out
于是可以在显示器上看到上述信息。
/////////////////////////////////////////////////////////////////////////////
ps1：test.cpp程序使用gprof得到的结果
Flat profile:
Each sample counts as 0.01 seconds.
%
cumulative
self
self
total
time
seconds
seconds
calls
ms/call
ms/call
name
60.00
0.09
0.09
50
1.80
1.80
test2(int)
40.00
0.15
0.06
50
1.20
1.20
test1(int)
%
the percentage of the total running time of the
time
program used by this function.
cumulative a running sum of the number of seconds accounted
seconds
for by this function and those listed above it.
self
the number of seconds accounted for by this
seconds
function alone.
This is the major sort for this
listing.
calls
the number of times this function was invoked, if
this function is profiled, else blank.
self
the average number of milliseconds spent in this
ms/call
function per call, if this function is profiled,
else blank.
total
the average number of milliseconds spent in this
ms/call
function and its descendents per call, if this
function is profiled, else blank.
name
the name of the function.
This is the minor sort
for this listing. The index shows the location of
the function in the gprof listing. If the index is
in parenthesis it shows where it would appear in
the gprof listing if it were to be printed.
Call graph (explanation follows)
granularity: each sample hit covers 4 byte(s) for 6.67% of 0.15 seconds
index % time
self
children
called
name
<spontaneous
[1]
100.0
0.00
0.15
main [1]
0.09
0.00
50/50
test2(int) [2]
0.06
0.00
50/50
test1(int) [3]
-----------------------------------------------
0.09
0.00
50/50
main [1]
[2]
60.0
0.09
0.00
50
test2(int) [2]
-----------------------------------------------
0.06
0.00
50/50
main [1]
[3]
40.0
0.06
0.00
50
test1(int) [3]
-----------------------------------------------
This table describes the call tree of the program, and was sorted by
the total amount of time spent in each function and its children.
Each entry in this table consists of several lines.
The line with the
index number at the left hand margin lists the current function.
The lines above it list the functions that called this function,
and the lines below it list the functions this one called.
This line lists:
index
A unique number given to each element of the table.
Index numbers are sorted numerically.
The index number is printed next to every function name so
it is easier to look up where the function in the table.
% time
This is the percentage of the `total' time that was spent
in this function and its children.
Note that due to
different viewpoints, functions excluded by options, etc,
these numbers will NOT add up to 100%.
self
This is the total amount of time spent in this function.
children
This is the total amount of time propagated into this
function by its children.
called
This is the number of times the function was called.
If the function called itself recursively, the number
only includes non-recursive calls, and is followed by
a `+' and the number of recursive calls.
name
The name of the current function.
The index number is
printed after it.
If the function is a member of a
cycle, the cycle number is printed between the
function's name and the index number.
For the function's parents, the fields have the following meanings:
self
This is the amount of time that was propagated directly
from the function into this parent.
children
This is the amount of time that was propagated from
the function's children into this parent.
called
This is the number of times this parent called the
function `/' the total number of times the function
was called.
Recursive calls to the function are not
included in the number after the `/'.
name
This is the name of the parent.
The parent's index
number is printed after it.
If the parent is a
member of a cycle, the cycle number is printed between
the name and the index number.
If the parents of the function cannot be determined, the word
`<spontaneous' is printed in the `name' field, and all the other
fields are blank.
For the function's children, the fields have the following meanings:
self
This is the amount of time that was propagated directly
from the child into the function.
children
This is the amount of time that was propagated from the
child's children to the function.
called
This is the number of times the function called
this child `/' the total number of times the child
was called.
Recursive calls by the child are not
listed in the number after the `/'.
name
This is the name of the child.
The child's index
number is printed after it.
If the child is a
member of a cycle, the cycle number is printed
between the name and the index number.
If there are any cycles （circles） in the call graph， there is an entry for the cycle-as-a-whole.
This entry shows who called thecycle （as parents） and the members of the cycle （as children.）The `+' recursive calls entry shows the number of function calls thatwere internal to the cycle， and the calls entry for each member shows，for that member， how many times it was called from other members ofthe cycle.
Index by function name
[3]
