char* line[256];   // An array of 256 pointers, sizeof(line) == 2048

##</code><code>##

char line[256];   // An array of 256 chars, sizeof(line) == 256

##</code><code>##

newSVpv(line, sizeof(line))   // length($line) == 2048 (or 256)

##</code><code>##

newSVpv(line, strlen(line))   // length($line) == 3
  -or-
newSVpv(line, 0)   // length($line) == 3

##</code><code>##

char* line = NULL;
ssize_t line_size;

while (1) {
    SV* line_sv;

    ssize_t len = getline(&line, &line_size, fh);
    if (len < 0)
        last;

    line_sv = newSVpvn(line, len);

    ...
}

if (line)
    free(line);

##</code><code>##

    while (1) {
        // Actually allocates at least 256.
        SV* line_sv = newSV(255);

        // We know line_sv has a string buffer, so we can use SvPVX.
        char* line = SvPVX(line_sv);

        if (!fgets(line, 256, fh)) {
            break;
        }

        SvCUR_set(line_sv, strlen(line));
        SvPOK_on(line_sv);

        ...

        // The callback may have changed line_sv,
        // so line might no longer be valid.
        line = SvPVbyte_nolen(line_sv);

        printf("c orig: %sc new: %s", line, modified_line);

        ...
    }