从文件中读取 1 个字节

Question

I need to read a single byte from a file. Normally when reading, I use a char array as the buffer. However, I need to be able to perform binary operations with byte, which can't be done with a char array. Here's what I've got:

read(file, buffer, 1);

I've tried making buffer both a char and an int, but both give me warnings that it expects a void * argument. But of course, that doesn't allow for binary operations like &.

How can I store buffer such that I can perform binary operations on it?

Answer 1

You could use the function int fgetc (FILE *fp) . The return value will be an int value from 0 to 255 or EOF .

Answer 2

Binary operation can be performed on char data type with unsigned . Even if its an array binary operation can be done to the single element of the array.

for your reference.

ssize_t read(int fd, void *buf, size_t count);

buffer has to be address of the character or character array , in your single char is sufficient. If you want to use array use the element array[0] and perform operation on that.

As mentioned in the comments above

unsigned char c; 
read(file, &c, 1);

Answer 3

你可以读入一个 char 数组，因为你（据说）知道如何做，然后对该数组的第一个元素执行二进制操作。

Answer 4

typedef unsigned char uint8_t; /* Not necessary if you are using C99, i.e. <stdint.h>. */

uint8_t buffer[BUF_SIZE] = {0};
    .
    .
    .
if (fread(buffer, sizeof(buffer[0]), 1, file) == 1)
{
    buffer[0] ^= 0xFFu; /* Or any other bit-wise operation. */
}

Refer -
1. https://linux.die.net/man/3/fread
2. http://en.cppreference.com/w/c/types/integer