Question

Here is my code :

char *name, name_log="log-";

——getting ‘name’ from user—–

strcat(name_log, name);
char ext[] = ".log";
strcat(name_log, ext);

What i need to end up with is name_log = “log-‘name’.log” but Im getting a segmentation fault error :((. What am I doing wrong and how can I fix it ? Thx

Answer 1

For a start, if this is your code:

char *name, name_log="log-";

then name_log is a char, not a char pointer.

Assuming that’s a typo, you cannot append to string literals like that. Modifications to string literals are undefined behaviour.

For a variable sized string, as user appears to be, probably the safest option is to allocate another string large enough to hold the result, something like:

char *name, *name_log = "log-", *ext = ".log";
// Do something to allocate and populate name
char *buffer = malloc (strlen (name_log) + strlen (name) + strlen (ext) + 1);
if (buffer == NULL) {
    // Out of memory.
} else {
    strcpy (buffer, name_log);
    strcat (buffer, name);
    strcat (buffer, ext);
    // Do something with buffer.
    free (buffer);
}

The malloc ensures you have enough space to do all the string operations safely, enough characters for the three components plus a null terminator.