[英]Reading bytes from binary file with 2 byte buffer
I am currently trying to read a file and calculate the frequencies of 1 byte equivalent numbers (0 to 255).我目前正在尝试读取文件并计算 1 字节等效数字(0 到 255)的频率。 I want to do the same for 2 byte equivalent numbers (0 to 65535)
我想对 2 字节等效数字(0 到 65535)做同样的事情
Simplified version of what I have:我所拥有的简化版本:
int length = 256; //any value 256>
long long values[length]
char buffer[length]
int i,nread;
fileptr = fopen("text.txt", "rb");
for (i=0; i<length; i++){ values[i]=0 }
while((nread = fread(buffer, 1, length, fileptr)) > 0){
for(i=0;i<nread;i++){
values[(unsigned char)buffer[i]]++;
}
}
fclose(fileptr);
for(i=0;i<length;i++{
printf("%d: %lld",i, values[i]);
}
What I am getting now:我现在得到的:
0: 21
1: 27
...
255: 19
What I want:我想要的是:
0: 4
1: 2
...
65535: 3
At the outset, let me correct what you have said.首先,让我纠正你所说的。 As of now you are not printing the frequencies of 2 byte range.
到目前为止,您还没有打印 2 字节范围的频率。 In general
unsigned char
is 1 byte (8 bits) and the results you are getting are also in accordance with what I said 8 bits => 0 <-> 2^8 -1 => 0 <-> 255
一般来说
unsigned char
是 1 个字节(8 位),你得到的结果也符合我所说的8 bits => 0 <-> 2^8 -1 => 0 <-> 255
For getting the frequencies of 16 bits range you can use u_int16_t
, Code goes something like this要获得 16 位范围的频率,您可以使用
u_int16_t
,代码如下
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main () {
FILE* fp = NULL;
/* Open file and setup fp */
int *freq = (int*) calloc(65536, sizeof(int));
u_int16_t value;
for ( ; ; ) {
if (read(fileno(fp), &value, sizeof(value)) < sizeof(value)) {
/* Assuming partial reads wont happen, EOF reached or data remaining is less than 2 bytes */
break;
}
freq[value] = freq[value] + 1;
}
for (int i = 0; i < 65536 ; i++) {
printf("%d : %d\n", i, freq[i]);
}
return 0;
}
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