need to prevent buffer overflows

[bsamuels]

I am new to C coming from C++ where the strings are easy and memory concerns are just where I parked my car.(Okay we do have new and delete and I check my vectors)
but all this character array stuff. anyway how do I check my buffer in this code to prevent overflow?

void do_text(char * path,int argi,char * argt[])
{
int out_fd, n_chars,i;
char buf[BUFFERSIZE];

if ( (out_fd = open(path,O_RDWR|O_APPEND)) == -1 )
{
oops("Cannot open logmesg\n","");

}

strcpy(buf,argt[1]);
strcat(buf," ");
for (i = 2;i < argi;i++) {
strcat(buf,argt[i]);
strcat(buf," ");
}
n_chars = strlen(buf);
if ( write( out_fd, buf, n_chars ) != n_chars)
perror(path);

if (close(out_fd) == -1 )
perror("Error closing files\n");


}

I'm just reading the command line and writing it to the file

[grady]

man strncpy, man strncat. But here it looks like you can just check with strlen to make sure argt[1] isn't going to overflow your array of length BUFFERSIZE.