C++: Unwanted Character in Output - c++

Question

I'm using libssh and I want to get some output from an executed command. It works for the most part, but I'm getting unwanted characters in the output. What am I doing wrong?
Example output for the command "test -f "/path/to/file" && echo found || echo not found"
not found
t foun
I want "not found", but not the line below it -- "t foun"
Where I think the problem is:
nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
while (nbytes > 0)
{
output.append(buffer, sizeof(buffer));
nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
}
Here's my function.
std::string exec_command(ssh_session session, const std::string& command)
{
ssh_channel channel;
int rc;
char* buffer;
std::string output;
int nbytes;
channel = ssh_channel_new(ssh_session);
if (channel == NULL)
return "Error";
rc = ssh_channel_open_session(channel);
if (rc != SSH_OK)
{
ssh_channel_free(channel);
return "Not Ok";
}
rc = ssh_channel_request_exec(channel, command.c_str());
if (rc != SSH_OK)
{
ssh_channel_close(channel);
ssh_channel_free(channel);
return "Not Ok";
}
nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
while (nbytes > 0)
{
output.append(buffer, sizeof(buffer));
nbytes = ssh_channel_read(channel, buffer, sizeof(buffer), 0);
}
if (nbytes < 0)
{
ssh_channel_close(channel);
ssh_channel_free(channel);
return "Error";
}
ssh_channel_send_eof(channel);
ssh_channel_close(channel);
ssh_channel_free(channel);
return output;
}

Answer 1

sizeof(buffer) means sizeof(char*) which is probably 4 bytes. In ssh_channel_read third parameter(count) is the limit of your buffer. Not the number of elements loaded in your buffer. You get it as a return value. So first, you need to allocate some memory for your buffer, lets say it 256 bytes:
const int BUFFER_SIZE = 256;
char buffer[BUFFER_SIZE];
Now you can pass buffer size as parameter and fill the buffer:
nbytes = ssh_channel_read(channel, buffer, BUFFER_SIZE, 0);
while (nbytes > 0)
{
output.append(buffer, nbytes);
nbytes = ssh_channel_read(channel, buffer, BUFFER_SIZE, 0);
}
And you need to append as much as you read which is nbytes.