How do I write characters out using Write() in C?

I'm trying to write a bitmap file to the browser in C. I can write the printable ascii parts like this,

write (socket, "BM", 2);

but how do I write the non-printable ones with their decimal value? I know that if I was writing to a file I could use something like this,

fprintf(fp, "%c%c%c%c" , 40,0,0,0);

But I don't know how to do the same thing but instead just write it to the socket... Please help me out, thank开发者_开发百科s.

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You can wrap a file descriptor in a FILE structure (thus enabling use of all the printf family) using fdopen():

int fd = socket(...);
FILE *fp = fdopen(fd, "w+");

Now, fp is just like any other FILE*. Cheers!

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If the bytes you want to write are static, you can simply define a buffer and use it...

char buffer[]={40,0,0,0};
write(socket, buffer, sizeof(buffer));

or inline...

write(socket, (char[]){40,0,0,0}, 4);

The best approach depends where the characters are coming from (are they dynamic / are they already in a buffer), how many there are, whether or not you want to do encoding, where the size element comes from.. etc etc..

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You can use sprintf for that.

char data[4];
sprintf(data, "%c%c%c%c", 40, 0, 0, 0);
write(socket, data, 4);

EDIT:

If you'r using this a lot, you can write your own function for formated write to socket like this:

void writef(int socket, const char * format, ...) {
    char buffer[1024];
    va_list args;
    va_start(args, format);
    int length = vsprintf(buffer, format, args);
    va_end(args);
    write(socket, buffer, length);
}

and then you can simply call writef(socket, "%c%c%c%c", 40, 0, 0, 0);

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You could snprintf the values into a char buffer, and then write out the buffer.