fread loses binary data - c++

Question

I am using fread function to read file, which I am sending via TCP. I found out, that fread doesn't read the whole file, if the file is binary. I tried everything what i found on the internet, but nothing helped. My code is:
#define BUFSIZE 1024
char buf[BUFSIZE];
FILE *file = fopen(soubor,"rb"); //I do a check which i won't write here
size_t bytes_loaded = 0;
while (!feof(file))
{
bytes_loaded = fread(buf,1,BUFSIZE,file);
if(bytes_loaded != BUFSIZE)
{
if(!feof(file))
{
for(int i = 0; i < 100;i++)
{
fseek(file,-strlen(buf),SEEK_CUR);
bytes_loaded = fread(buf,1,BUFSIZE,file);
if(bytes_loaded == BUFSIZE)
{
break;
}
else if(i == 99)
{
fprintf(stderr,"C could't read the file\n");
fclose(file);
close(client_socket);
return 1;
}
}
}
}
bytestx = send(client_socket, buf, BUFSIZE, 0);
if (bytestx < 0)
perror("ERROR in sendto");
bzero(buf, BUFSIZE);
bytes_loaded = 0;
}
Am I doing something wrong? For example that fread check...

Answer 1

Your whole fread() error handling is wrong, get rid of it (using strlen() on a binary buffer is wrong anyway).
In fact, you shouldn't be using feof() to control your loop. Simply call fread() in a loop until it returns < 1 on EOF or error (use feof() and ferror() to differentiate). And when it returns > 0, you need to pass that value to send instead of passing BUFSIZE.
Try something more like this:
#define BUFSIZE 1024
char buf[BUFSIZE], *pbuf;
FILE *file = fopen(soubor, "rb");
...
size_t bytes_loaded;
do
{
bytes_loaded = fread(buf, 1, BUFSIZE, file);
if (bytes_loaded < 1)
{
if ((!feof(file)) && ferror(file))
fprintf(stderr, "Couldn't read the file\n");
break;
}
pbuf = buf;
do
{
bytestx = send(client_socket, pbuf, bytes_loaded, 0);
if (bytestx < 0)
{
perror("ERROR in send");
break;
}
pbuf += bytestx;
bytes_loaded -= bytestx;
}
while (bytes_loaded > 0);
}
while (bytes_loaded == 0);
fclose(file);
...

Answer 2

If you are just shifting bytes from the file to the socket then you can just keep looping on the return value from std::fread which tells you how many bytes you read and then send exactly that many bytes to your send() command.
Something like this (untested) code:
if(FILE* fp = std::fopen(soubor, "rb"))
{
char buf[1024];
std::size_t bytesrx;
while((bytesrx = std::fread(0, 1, sizeof(buf), fp)) > 0)
{
int bytestx;
if((bytestx = send(client_socket, buf, bytesrx, 0) < 0))
{
// socket error
std::cout << "socket error: " << std::strerror(errno) << '\n';
return EXIT_FAILURE;
}
}
if(bytesrx < 0)
{
// file error
std::cout << "file error: " << std::strerror(errno) << '\n';
return EXIT_FAILURE;
}
}
else
{
// error opening file
}