C：来自二进制文件的fread与原始模式不匹配后存储到缓冲区中的unsigned short

Question

I have a binary file filled with 2-byte words following this pattern(in HEX): 0XY0. this is the part of the code where I execute fread and fopen.

unsigned short buffer[bufferSize]; 
FILE *ptr;                          //

ptr = fopen(fileIn,"rb");           //

if(ptr == NULL)
{
    fprintf(stderr,"Unable to read from file %s because of %s",fileIn,strerror(errno));
    exit(20);
}

size_t readed = fread(buffer,(size_t)sizeof(unsigned short),bufferSize,ptr);
if(readed!=bufferSize)
{
    printf("readed and buffersize are not the same\n");
    exit(100);
}
//---------------------------

If I look at any content of the buffer, for example buffer[0], instead of being a short with pattern 0XY0, it is a short with pattern Y00X Where is my error? is it something regarding endianess? of course i checked every element inside buffer. the program execute with no errors.

EDIT: If i read from file with size char instead of short, the content of buffer(obviously changed to char buffer[bufferSize*2];) match the pattern OXYO. So I have that (for example) buffer[0] is 0X and buffer[1] is Y0

Answer 1

Your problem seems to be exactly typical of an endianness mismatch between the program that stored the data into the file and the one that reads it. Remember that mobile phone processors tend to use big-endian representations and laptop little-endian.

Another potential explanation is your file might have been written in text mode by a windows based program that converted the 0x0A bytes into pairs of 0x0D / 0x0A , causing the contents to shift and cause a similar pattern as what you observe.

Instead of reading the file with fread , you should read it byte by byte and compute the values according the endianness specified for the file format.