Tim Moore

I'm working on my first Max external, and I need to do some file I/O. Reading the Max SDK documentation on 

void myobject_doread(t_myobject *x, t_symbol *s)
{
    t_fourcc filetype = 'TEXT', outtype;
    short numtypes = 1;
    char filename[MAX_PATH_CHARS];
    short path;
 
    if (s == gensym("")) {      // if no argument supplied, ask for file
        if (open_dialog(filename, &path, &outtype, &filetype, 1))       // non-zero: user cancelled
            return;
    } else {
        strcpy(filename, s->s_name);    // must copy symbol before calling locatefile_extended
        if (locatefile_extended(filename, &path, &outtype, &filetype, 1)) { // non-zero: not found
            object_error(x, "%s: not found", s->s_name);
            return;
        }
    }
    // we have a file
    myobject_openfile(x, filename, path);
}

My C is rusty, but I know that strcpy can cause buffer overruns if the source string is longer than the destination array.

 has different advice: "use strncpy_zero() to copy the contents of a t_symbol to a character string first, as shown below:"

char filename[MAX_FILENAME_CHARS]; 
strncpy_zero(filename,str->s_name, MAX_FILENAME_CHARS); 
result = locatefile_extended(filename,&path,&type,typelist,1);

 is a bit vague: "Copy the contents of one string to another, in a manner safer than the standard strcpy() or strncpy(). This is the prefered function to use for this operation in Max."

In what way is it safer? From the name, I assume it guarantees that the destination string will be null terminated, which standard strncpy does not in the case where the source is longer than the specified size. But then how can I detect that case, which would result in an incorrect filename? The example code doesn't seem to handle it.

I'm working on my first Max external, and I need to do some file I/O. Reading the Max SDK documentation on file handling, I saw this example code:

The documentation for locatefile_extended has different advice: "use strncpy_zero() to copy the contents of a t_symbol to a character string first, as shown below:"

The documentation for strncpy_zero is a bit vague: "Copy the contents of one string to another, in a manner safer than the standard strcpy() or strncpy(). This is the prefered function to use for this operation in Max."

I'm working on my first Max external, and I need to do some file I/O. 

safe-string-copies-using-strncpy_zero

Bumping this thread because I realised I accidentally posted it in the Misc forum instead of Dev (now updated). Can anyone explain exactly what strncpy_zero does differently than strncpy?

Safe string copies using strncpy_zero