我已经尝试从谷歌、论坛、维基百科和很多很多论坛搜索这个功能超过两个小时，但我找不到它。我怎么能做到这一点？我尝试了以下但没有奏效。
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <stdint.h>
static unsigned int mylog2 (unsigned int val) {
unsigned int ret = -1;
while (val != 0) {
val >>= 1;
ret++;
}
return ret;
}
int main(int argc, char **argv)
{
FILE *pFile;
int i; // various loop index
int j; // filename loop index
int n; // Bytes read by fread;
int size; // Filesize
float entropy;
float temp; // temp value used in entropy calculation
long alphabet[256];
unsigned char buffer[1024];
/* do this for all files */
for(j = 1; j < argc; j++)
{
/* initialize all values */
size = 0;
entropy = 0.0;
memset(alphabet, 0, sizeof(long) * 256);
pFile = fopen(argv[j], "rb");
if(pFile == NULL)
{
printf("Failed to open `%s`\n", argv[j]);
continue;
}
/* Read the whole file in parts of 1024 */
while((n = fread(buffer, 1, 1024, pFile)) != 0)
{
/* Add the buffer to the alphabet */
for (i = 0; i < n; i++)
{
alphabet[(int) buffer[i]]++;
size++;
}
}
fclose(pFile);
/* entropy calculation */
for (i = 0; i < 256; i++)
{
if (alphabet[i] != 0)
{
temp = (float) alphabet[i] / (float) size;
entropy += -temp * mylog2(temp);
}
}
printf("%02.5f [ %02.5f ]\t%s\n", entropy, entropy / 8, argv[j]);
} // outer for
return 0;
}
我知道我做错了。在python中它似乎要容易得多，在python中它是：
import sys
import math
if len(sys.argv) != 2:
print "Usage: file_entropy.py [path]filename"
sys.exit()
# read the whole file into a byte array
f = open(sys.argv[1], "rb")
byteArr = map(ord, f.read())
f.close()
fileSize = len(byteArr)
print 'File size in bytes:'
print fileSize
print
# calculate the frequency of each byte value in the file
freqList = []
for b in range(256):
ctr = 0
for byte in byteArr:
if byte == b:
ctr += 1
freqList.append(float(ctr) / fileSize)
# print 'Frequencies of each byte-character:'
# print freqList
# print
# Shannon entropy
ent = 0.0
for freq in freqList:
if freq > 0:
ent = ent + freq * math.log(freq, 2)
ent = -ent
print 'Shannon entropy (min bits per byte-character):'
print ent
print
print 'Min possible file size assuming max theoretical compression efficiency:'
print (ent * fileSize), 'in bits'
print (ent * fileSize) / 8, 'in bytes'
### Modifications to file_entropy.py to create the Histogram start here ###
### by Ken Hartman www.KennethGHartman.com
import numpy as np
import matplotlib.pyplot as plt
N = len(freqList)
ind = np.arange(N) # the x locations for the groups
width = 1.00 # the width of the bars
#fig = plt.figure()
fig = plt.figure(figsize=(11,5),dpi=100)
ax = fig.add_subplot(111)
rects1 = ax.bar(ind, freqList, width)
ax.set_autoscalex_on(False)
ax.set_xlim([0,255])
ax.set_ylabel('Frequency')
ax.set_xlabel('Byte')
ax.set_title('Frequency of Bytes 0 to 255\nFILENAME: ' + sys.argv[1])
plt.show()
如何在 C++ 中实现相同的功能？希望有人如实回答。