C++ Dll string function crash - c++

Question

I have the following problem.
I use the following function to receive a string from a buffer until a newline occurs.
string get_all_buf(int sock) {
int n = 1, total = 0, found = 0;
char c;
char temp[1024*1024];
string antw = "";
while (!found) {
n = recv(sock, &temp[total], sizeof(temp) - total - 1, 0);
if (n == -1) {
break;
}
total += n;
temp[total] = '\0';
found = (strchr(temp, '\n') != 0);
if (found == 0){
found = (strchr(temp, '\r\n') != 0);
}
}
antw = temp;
size_t foundIndex = antw.find("\r\n");
if (foundIndex != antw.npos)
antw.erase ( antw.find ("\r\n"), 2 );
foundIndex = antw.find("\n");
if (foundIndex != antw.npos)
antw.erase ( antw.find ("\n"), 2 );
return answ;
}
So use it like this:
string an = get_all_buf(sClient);
If I create an exe file everything works perfectly.
But if I create a dll and run it using rundll32 the application closes at "string an = get_all_buf(sClient);" without any error message...
I tried to fix this for hours now, and I am currently a bit desperate...
P.S. sorry for obvious errors or bad coding style, I just started learning C++.

Answer 1

char temp[1024*1024];
declares a 1Mb structure on the stack. This may be too large and overflow available stack memory. You could instead give it static scope
static char temp[1024*1024];
or allocate it dynamically
char* temp = (char*)malloc(1024*1024);
// function body
free(temp);
Alternatively, assuming the mention of run32.dll means you're working on Windows, you could investigate keeping it on the stack by using the /STACK linker option. This probably isn't the best approach - you've already found it causes problems when you change build settings or try to target other platforms.

Answer 2

Instead of creating temp variable on the stack, I'd create it dynamically (on the heap), but not using raw malloc and free as showed in a previous answer, but using modern C++ and std::vector:
#include <vector>
std::vector<char> temp(1024*1024);
This is exception safe, and you don't have to pay attention to release the allocated memory: std::vector's destructor will do that automatically (also in case of exceptions thrown).
Instead of sizeof(temp), in your code you can use temp.size() (which will return the count of elements in the vector, and since this is a vector of chars, it will return just the total vector size in chars i.e. in bytes).
You can still use operator[] for std::vector, as you do for raw C arrays.
Note also that if you are building a DLL and the above function is exposed at the DLL interface, since this function has a C++ interface with a STL class (std::string) at the boundary, you must pay attention that both your DLL and your clients are built with dynamic linking to the same CRT, and with the same compiler and the same compiler settings (e.g. you can't mix a DLL built with VS2008/VC9 with a .EXE built with VS2010/VC10, or a release-build DLL with a debug-build EXE built with the same compiler).