Why doesn't my base64 string get fully sent/received in C++ socket

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C++

sockets

Hello, This is my first time trying to write an actual program in C++

my program communicates using sockets and I faced some problems, I tried to implement file transfer functionality. when I used to code similar programs in python I would first encode the data of the file in base64 and decode it on the other side, so I tried doing that here.

but for some reason the base64 string does get sent or received as the full string. I only get the first part of the string but the rest is lost.

What I have tried:

I tried writing my own send and receive functions because I thought it might be a size problem, but that resulted in the same behavior.

the send function (called "sendAll") takes a vector that is a string split to chunks by another function I found online, and then sends one after another to the socket, and then sends a special string "<end_of_socket_data>".

the receive function (called "recvAll") receives the data one after another and puts them all together and then gives them back to me after it received the special string "<end_of_socket_data>".

I will post the functions in case these were of any interest.

sendAll:

int sendAll(int socket, vector<string> ls, int flag)
{
    int total_size;
    int size_now;
    string str;

    for(int i = 0; i < ls.size(); i++) {
        str = ls.at(i);
        size_now = send(socket, str.c_str(), sizeof(str.c_str()), flag);

        MessageBox(NULL, str.c_str(), "Data", MB_OK);

        total_size += size_now;

    }
    char end_message[100] = "<END_OF_SOCKET_DATA>";

    send(socket, end_message, sizeof(end_message), 0);

    return total_size;
}

recvAll:

int recvAll(int socket, string& full_str)
{
	full_str = "";

	int total_size = 0;
	int size_now = 0;
	char chunk[CHUNK_SIZE];

	while(1) {

		bzero(chunk, sizeof(chunk));

		size_now = recv(socket, chunk, sizeof(chunk), 0);

		if(strcmp(chunk, "<END_OF_SOCKET_DATA>") == 0)
		{
			break;
		}
		else
		{		
			full_str += chunk;

			total_size += size_now;
		}

	}
	return total_size;

}