Base64 file encode - fstream

I found a library for base64 encode/decode of strings.
I added a function myself for encoding files - base64_file using the above.
My idea is to perform this action on files stored on an sd card.
The problem is that the code required “fstream” which I cant figure out how to include.
The error is:

sketch\base64.cpp:3:20: fatal error: fstream: No such file or directory

#include

base64.h :

#include <string.h>

std::string base64_encode(unsigned char const*, unsigned int len);
std::string base64_decode(std::string const& s);
std::string  base64_file(char* filename);

base64.cpp :

#include "base64.h"

#include <fstream> 
#include <sstream>


static const std::string base64_chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";

static inline bool is_base64(unsigned char c) {
	return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len) {
	std::string ret;
	int i = 0;
	int j = 0;
	unsigned char char_array_3[3];
	unsigned char char_array_4[4];

	while (in_len--) {
		char_array_3[i++] = *(bytes_to_encode++);
		if (i == 3) {
			char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
			char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
			char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
			char_array_4[3] = char_array_3[2] & 0x3f;

			for (i = 0; (i <4); i++)
				ret += base64_chars[char_array_4[i]];
			i = 0;
		}
	}

	if (i)
	{
		for (j = i; j < 3; j++)
			char_array_3[j] = '\0';

		char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
		char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
		char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
		char_array_4[3] = char_array_3[2] & 0x3f;

		for (j = 0; (j < i + 1); j++)
			ret += base64_chars[char_array_4[j]];

		while ((i++ < 3))
			ret += '=';

	}

	return ret;

}

std::string base64_decode(std::string const& encoded_string) {
	int in_len = encoded_string.size();
	int i = 0;
	int j = 0;
	int in_ = 0;
	unsigned char char_array_4[4], char_array_3[3];
	std::string ret;

	while (in_len-- && (encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
		char_array_4[i++] = encoded_string[in_]; in_++;
		if (i == 4) {
			for (i = 0; i <4; i++)
				char_array_4[i] = base64_chars.find(char_array_4[i]);

			char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
			char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
			char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

			for (i = 0; (i < 3); i++)
				ret += char_array_3[i];
			i = 0;
		}
	}

	if (i) {
		for (j = i; j <4; j++)
			char_array_4[j] = 0;

		for (j = 0; j <4; j++)
			char_array_4[j] = base64_chars.find(char_array_4[j]);

		char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
		char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
		char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

		for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
	}

	return ret;
}

std::string  base64_file(char* filename){
	/* File exists check */
	std::ostringstream ss;
	ss << filename;
	
	std::ifstream f(ss.str());
	if (!f.good()){
		//std::cout << "File " << ss.str()  << " does not exist!" << std::endl;
		exit;
	}
	
	/* Read file to string */
	std::ifstream fin(filename, std::ios::in | std::ios::binary);
	std::ostringstream oss;
	oss << fin.rdbuf();
	std::string data(oss.str());


	/* Convert string to base64 */
	const std::string binary_string = oss.str();
	return base64_encode(reinterpret_cast<const unsigned char*>(binary_string.c_str()), binary_string.length());

}

I included GitHub - maniacbug/StandardCplusplus: Standard C++ for Arduino (port of uClibc++) to my scetch which actually has the file fstream, but still get the error !?

Has anyone ever did anything similar?
How would be the performance of such operation having the limited ram on arduino?

this may help

http://www.cplusplus.com/doc/tutorial/files/

The examples still use fstream.