我一直在使用gprof来尝试让我的C程序更快。目前，它的时间约为3秒，但这正是gprof给我的：
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
100.40 0.01 0.01 3842 0.00 0.00 insertObject
0.00 0.01 0.00 146307 0.00 0.00 getBits
0.00 0.01 0.00 1 0.00 0.00 initialize
0.00 0.01 0.00 1 0.00 10.04 lzw_decode
% 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.
Copyright (C) 2012 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
Call graph (explanation follows)
granularity: each sample hit covers 2 byte(s) for 99.60% of 0.01 seconds
index % time self children called name
0.01 0.00 3842/3842 lzw_decode [2]
[1] 100.0 0.01 0.00 3842 insertObject [1]
-----------------------------------------------
0.00 0.01 1/1 main [3]
[2] 100.0 0.00 0.01 1 lzw_decode [2]
0.01 0.00 3842/3842 insertObject [1]
0.00 0.00 146307/146307 getBits [4]
0.00 0.00 1/1 initialize [5]
-----------------------------------------------
<spontaneous>
[3] 100.0 0.00 0.01 main [3]
0.00 0.01 1/1 lzw_decode [2]
-----------------------------------------------
0.00 0.00 146307/146307 lzw_decode [2]
[4] 0.0 0.00 0.00 146307 getBits [4]
-----------------------------------------------
0.00 0.00 1/1 lzw_decode [2]
[5] 0.0 0.00 0.00 1 initialize [5]
-----------------------------------------------
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 is 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 the
cycle (as parents) and the members of the cycle (as children.)
The `+' recursive calls entry shows the number of function calls that
were internal to the cycle, and the calls entry for each member shows,
for that member, how many times it was called from other members of
the cycle.
Copyright (C) 2012 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
Index by function name
[4] getBits [1] insertObject
[5] initialize [2] lzw_decode
gprof之前似乎对我有用，所以我不确定发生了什么。这是我的makefile：
CC = gcc
CFLAGS = -g3 -std=c99 -pedantic -Wall -g -pg
HWK = /c/cs323/Hwk2/
objects = code1.o lzw.o
lzw: lzw.o
${CC} ${CFLAGS} -o lzw lzw.o
encode: lzw.o
${CC} ${CFLAGS} -o encode lzw.o
decode: lzw.o
${CC} ${CFLAGS} -o decode lzw.o
lzw.o: lzw.c ${HWK}code1.c
${CC} ${CFLAGS} -c lzw.c ${HWK}code1.c
这里是insertObject：
void insertObject (int pref, int ch)
{
struct node x;
if (ch < 0)
{
ch=4096-ch;
}
x.chr=ch;
x.pref=pref;
int i;
i = 256;
while ((i<4096)&&(hashtable[i].chr!=(0)))
{
i++;
}
hashtable[i]=x;
}
答案 0 :(得分：0)
如果你阅读了gprof文档here，你就会知道真正如何描述执行时间。再说一遍，我并不是说它可能都是错的，但它很有可能显示出正确的时间
我知道这一开始可能会让人感到困惑，我建议的是使用其他一些分析器。很多选择
答案 1 :(得分：0)
gprof仅显示在使用-pg选项编译的代码中花费的时间。首先检查在将-pg添加到Makefile时是否实际重新编译了所有代码。最好是包含这样的目标clean：
clean:;
rm -f lzw encode decode ${objects}
然后使用make clean lzw重建。
如果它没有帮助，可能会在某些库中花费时间。在这种情况下，您需要下载使用profiler选项编译的libc或自行编译。包含配置文件libc的软件包很少。我找到了这两个：glibc-profile和libc6-prof，它们似乎没有系统地包含在发行版中。安装此类软件包后，您需要添加选项-static-libgcc -lc_p并重新编译。
如果它仍然没有帮助，你将必须检查哪些其他库链接到你的程序，时间可能花在那里。