C++ memory leaks when read binary file - c++

Question

I wrote the program automatically sends the compressed files to the server.
Files are sent with a weak VPS that the disposal has 1.5 GB of RAM.
When the load binary files gets micro memory leaks, but at 30 000 .pdf refuses to continue allocating memory.
I did a little deception because it saves log and run the program again, cleaning RAM in this way, however, would like to know why. Mark that if I do not do 'ios: binary', such leaks are not.
My code :
std::ifstream ifs(url,ios::binary);
std::string content((std::istreambuf_iterator<char>(ifs)), (std::istreambuf_iterator<char>()));
content = PFHelper::stream_compression(content);
content = PFHelper::ASE_encodeCppStandard(content,KS,PFHelper::AES_CBC_128);
PFHelper::stream_compression
std::string PFHelper::stream_compression(std::string stream)
{
z_stream zs; // z_stream is zlib's control structure
memset(&zs, 0, sizeof(zs));
if (deflateInit(&zs, Z_BEST_COMPRESSION) != Z_OK)
{
throw new PFException(L"EXCEPTION_DURING_ZLIB_COMPRESSION");
}
zs.next_in = (Bytef*)stream.data();
zs.avail_in = stream.size(); // set the z_stream's input
int ret;
char outbuffer[32768];
std::string outstring;
// retrieve the compressed bytes blockwise
do {
zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
zs.avail_out = sizeof(outbuffer);
ret = deflate(&zs, Z_FINISH);
if (outstring.size() < zs.total_out) {
// append the block to the output string
outstring.append(outbuffer,
zs.total_out - outstring.size());
}
} while (ret == Z_OK);
deflateEnd(&zs);
if (ret != Z_STREAM_END) { throw new PFException(L"EXCEPTION_DURING_ZLIB_COMPRESSION"); }
return outstring;
}
PFHelper::ASE_encodeCppStandard
std::string PFHelper::ASE_encodeCppStandard(std::string in, wchar_t* KS ,wchar_t* typ)
{
string ctext = "";
std::string KS_string = PFHelper::ConvertFromUtf8ToString(KS);
if (typ == PFHelper::AES_CBC_128)
ctext = encrypt(KS_string,in);
if (typ == PFHelper::AES_CBC_256)
ctext = encryptEX(KS_string, in);
return ctext;
}
static string encrypt(string KS, const string ptext)
{
EVP_CIPHER_CTX* ctx;
ctx = EVP_CIPHER_CTX_new();
int rc = EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, (byte*)&KS[0], (byte*)&KS[0]);
if (rc != 1)
throw runtime_error("EVP_EncryptInit_ex failed");
// Cipher text will be upto 16 bytes larger than plain text
std::string ctext;
ctext.resize(ptext.size()+16);
int out_len1 = (int)ctext.size();
rc = EVP_EncryptUpdate(ctx, (byte*)&ctext[0], &out_len1, (const byte*)&ptext[0], (int)ptext.size());
if (rc != 1)
throw runtime_error("EVP_EncryptUpdate failed");
int out_len2 = (int)ctext.size() - out_len1;
rc = EVP_EncryptFinal_ex(ctx, (byte*)&ctext[0] + out_len1, &out_len2);
if (rc != 1)
throw runtime_error("EVP_EncryptFinal_ex failed");
ctext.resize(out_len1 + out_len2);
return ctext;
}