Array isn't free'd after going out of scope - c++

Question

I have a simple char array used to read from a pipe.
This array is used in an infinite while cycle
int main()
{
mkfifo("process1_write", 0666);
mkfifo("process1_read", 0666);
int fd1,fd2;
fd1 = open(process1_write, O_RDWR);
fd2 = open(process1_read, O_RDONLY| O_NONBLOCK);
std::string outmsg = "{process: drv_rtnode_1, message: hi}";
while (1)
{
char str1[1050];
printf("cycle %d\n\t",i++);
int in = read(fd2, str1, 1024);
if(in>0)
{
printf("message: %s, in: %d\n", str1, in);
write(fd1, outmsg.c_str(), outmsg.size());
}
else
printf("No content received\n");
sleep(1);
}
return 0;
}
As you can see, str1 is instantiated on the stack as a local variable so I'd expect it to be free'd after each while-cycle.
However what I get is the following:
Cycle 1: receiving data from the PIPE, thus enterning if(in>0)
message: {"msg type": "status inst", "ProcessName": "process1", "StatusDetail": "dettaglio componente"}{"msg type": "status ses", "ProcessName": "process1", "GroupName": "MOT", "GroupSts": "Online", "ActiveSession": "PRI", "StatusDetail": "dettaglio sessione"}, in: 251
in = 251, so it's counting the number of characters correctly
Cycle 2: receiving LESS data from the PIPE
This time I'm receiving this message: {"state":"alive"}
But here's the printed output:
message: {"state":"alive"}tus inst", "ProcessName": "process1", "StatusDetail": "dettaglio componente"}{"msg type": "status ses", "ProcessName": "process1", "GroupName": "MOT", "GroupSts": "Online", "ActiveSession": "PRI", "StatusDetail": "dettaglio sessione"} , in: 17
in = 17, so the number of characters is, once again, correctly counted but my array has not been emptied at all
This happens no matter what kind of data I receive.
I also tried changing the code as follows:
char* str1 = new char[1050];
while (1)
{
printf("cycle %d\n\t",i++);
int in = read(fd2, str1, 1024);
if(in>0)
{
printf("message: %s, in: %d\n", str1, in);
write(fd1, outmsg.c_str(), outmsg.size());
}
else
printf("No content received\n");
sleep(1);
delete[] str1;
str1 = new char[1050];
}
But nothing has changed. It behaves exactly the same.

Answer 1

The following:
while (1)
{
char str1[1050];
allocates on the function call stack, but does it like this:
char str1[1050];
while (1)
{
So the location is reused, and only about 1050 bytes callocated.
The problem is, that for strings a nul terminator is needed:
int in = read(fd2, str1, 1024);
if (in > 0)
{
str1[in] = '\0';
Now the overwriting with shorter data does not show prior reads.