How to prevent buffer overflow in C/C++?
- by alexpov
Hello, i am using the following code to redirect stdout to a pipe, then read all the data from the pipe to a buffer. I have 2 problems:
first problem: when i send a string (after redirection) bigger then the pipe's BUFF_SIZE, the program stops responding (deadlock or something).
second problem: when i try to read from a pipe before something was sent to stdout. I get the same response, the program stops responding - _read command stuck's ...
The issue is that i don't know the amount of data that will be sent to the pipe after the redirection.
The first problem, i don't know how to handle and i'll be glad for help. The second problem i solved by a simple workaround, right after the redirection i print space character to stdout. but i guess that this solution is not the correct one ...
#include <fcntl.h>
#include <io.h>
#include <iostream>
#define READ 0
#define WRITE 1
#define BUFF_SIZE 5
using namespace std;
int main()
{
int stdout_pipe[2];
int saved_stdout;
saved_stdout = _dup(_fileno(stdout)); // save stdout
if(_pipe(stdout_pipe,BUFF_SIZE, O_TEXT) != 0 ) // make a pipe
{
exit(1);
}
fflush( stdout );
if(_dup2(stdout_pipe[1], _fileno(stdout)) != 0 ) //redirect stdout to the pipe
{
exit(1);
}
ios::sync_with_stdio();
setvbuf( stdout, NULL, _IONBF, 0 );
//anything sent to stdout goes now to the pipe
//printf(" ");//workaround for the second problem
printf("123456");//first problem
char buffer[BUFF_SIZE] = {0};
int nOutRead = 0;
nOutRead = _read(stdout_pipe[READ], buffer, BUFF_SIZE); //second problem
buffer[nOutRead] = '\0';
// reconnect stdout
if (_dup2(saved_stdout, _fileno(stdout)) != 0 )
{
exit(1);
}
ios::sync_with_stdio();
printf("buffer: %s\n", buffer);
}
Thanks,
Alex
