Empty string input with read system call causes Segmentation Fault

Question

I'm trying to read in input from STDIN using read(int fd, void *buf, size_t count); How should I handle cases when the input is EOF? Or empty string? Currently, I get a Segmentation Fault

Here is the code snippet:

int rd;
char buf[100];
rd = read(0, buf, 99);
buf[strcspn(buffer, "\n")] = 0;

Thanks

Answer 1

Like all other string functions, strcspn relies on the string to be null-terminated to begin with.

If the input doesn't contain a newline, then the strcspn function will go out of bounds due to the lack of the terminator.

You also need to handle the case when read returns with end-of-file or error, which is indicated by it returning 0 or -1 (respectively). Just as specified in the manual (which you really should read!).

Simply add the terminator directly after the read call at the appropriate position, but only if read succeeds:

rd = read(STDIN_FILENO, buf, sizeof buf - 1);  // sizeof buf relies on buf being an actual array and not a pointer
if (rd == -1)
{
    // Error, handle it
}
else if (rd == 0)
{
    // End of file, handle it
}
else
{
    // Read something

    buf[rd] = '\0';  // Terminate string

    // Terminate a newline
    buf[strcspn(buf, "\n")] = '\0';  // Truncate at newline (if any)
}