How to send() an image by saving it in char string in ANSI C? Problem with casting

I'm writing my own server in ANSI C (on Linux) and I've got one problem with sending images to a web browser. I'm using the function "send()" to send it and it required a char *. So I was reading a file char by char (using fgetc), I used fread and fgets, but everything had a problem with casting the content(int in most cases) to a bufor - some bytes still were missing (e.g 2008 was send instead of 2020). I think there is some problem with conversion, but I used sprintf and wchar_t and it is still not working.

I've got a function:

void send_www(char *buff, int cd){      
if(send (cd, buff, strlen(buff), 0) < 0) {
        perror ("send()");
        exit (1);

which I use here:

//  while (fread(znak, sizeof(char), i,  handler) != 0) {
    for (j = 0; j < i; j++) {
    a = fgetc(handler);
    sprintf(znak, "%ls", a);
    send_www(znak, cd);
    }

where i is the length of the image file, znak is the char* (in this version wc开发者_StackOverflow社区har_t*). You can also see my earlier try of using fread.

It's hard to say without more details - can you post some code?

One thing is to make sure you open the image file with the binary option, e.g. fopen(filename, "rb");

If you're just reading a binary file and sending it to a socket where the other end is expecting binary you should not need any casting or sprintf.

You seem to be confusing char type with strings. A C string is a sequence of characters that is zero terminated. Your image file is a binary file containing a sequence of characters but it is not a string. The send() function takes a pointer to a sequence of bytes, not strings. To illustrate this look at this sequence of chars (or bytes):

255, 255, 255, 0, 0, 0, 255, 255, 255

In some image file formats this can be three RGB pixels, so white, black white. 9 bytes. Can be held in a char buffer[9] . If you call strlen() on this you will get the result 3. strlen() counts until it sees a zero character. If you read these bytes from a file without the binary flag it may get transformed and you may get less or more bytes than are really in the file (depending on the contents, the OS etc.).

Rough explanatory code follows:

char buffer[1024];
FILE *infile = fopen("test.gif", "rb"); // open a file (check for failure in real code)
int nread = fread(buffer, 1, 1024, infile);
// assume socket is connected (check for number of bytes sent or error in real code)
send(socket, buffer, nread, 0); 
fclose(infile); // close the file

To read from a binary file and send the data out to a socket you need to do something like the snippet above. You would probably keep reading until you reach the end of file, the snippet only reads once. Also in real code you should check to see how many bytes were actually sent (in the return value from send) and keep calling send until you've sent all the data or an error has occured.

You are using strlen(). strlen() stops and returns the size after it reaches a \0 byte. Images and binary data are allowed to have a byte valued zero anywhere, so strlen() is useless in those cases.

You need to modify your function to:

send_www(unsigned char *buff, size_t buf_len int cd);

And pass the image size to it, so you can safely send() it with the appropriate size.

In your case, it seems you are sure it is a wchar_t string, use the appropriate function, wcslen(), not strlen() :)

I'd guess that the problem is that your image data contain characters (\0), so they aren't being sent because you're using strlen() to figure out how much data to send.