C char pointer problem weird values concatonated toward the end - c

Question

Hi I am having trouble with this function. For some reason weird values are appended to the string at random times.
/* ex: path = /usr/src/data returns: /usr/src */``
char* get_pathname(char* path) {
char* pathname;
char* temp;
int filenamelength;
int pathlength;
temp = get_filename(path); //name of file within original path
filenamelength = strlen(temp);
printf("strlen(temp) %d\n", strlen(temp));
printf("strlen(path) %d\n", strlen(path));
pathlength = strlen(path);
pathname = malloc((pathlength-filenamelength-1));
strncpy(pathname, path, pathlength-filenamelength-1);
return pathname;
}
/* ex: path /usr/src/data returns: data */
char* get_filename(char* path) {
char* get_filename(char* path){
char* filename;
char* temp = strrchr(path, '/')+1; //name of file within original path
filename = malloc(sizeof(char) * (strlen(path) + 1));
strcpy(filename, temp);
return filename;
}

Answer 1

strncpy doesn't 0-terminate when the copied string is larger than or exactly fits the passed size.
pathname = malloc((pathlength-filenamelength-1));
strncpy(pathname, path, pathlength-filenamelength-1);
Change to:
pathname = malloc(pathlength-filenamelength);
^^^
strncpy(pathname, path, pathlength-filenamelength-1);
pathname[pathlength-filenamelength-1] = 0;

Answer 2

static void *
xmalloc(size_t n)
{
void *obj = malloc(n);
if (obj == NULL) {
perror("xmalloc");
exit(EXIT_FAILURE);
}
return obj;
}
char *
get_pathname(const char *path)
{
char *slash = strrchr('/', path);
if (slash == NULL) {
char *dot = xmalloc(2);
strcpy(dot, ".");
return dot;
}
char *parent = xmalloc((slash - path) + 1);
memcpy(parent, path, slash - path);
parent[slash - path] = '\0';
return parent;
}
char *
get_filename(const char *path)
{
const char *slash = strrchr('/', path);
const char *filename = (slash == NULL) ? "" : (slash + 1);
char *result = xmalloc(strlen(filename) + 1);
strcpy(result, filename);
return result;
}
I've added the missing error handling and the cases when there is no slash in the given path. In your original code you had a memory leak in get_pathname: you called malloc via get_filename, but didn't free this memory after you used it.

Answer 3

Will this work for you?
char *get_path(char *path)
{
char *fpath = NULL;
char *slash = NULL;
if(path == NULL) goto error;
fpath = strdup(path);
if(fpath == NULL) goto error;
slash = strrchr(fpath, '/');
if(slash != NULL) *slash = '\0';
error:
return fpath;
}
char *get_filename(char *path)
{
char *slash = NULL;
char *fname = NULL;
if(path == NULL) goto error;
slash = strrchr(path, '/');
fname = (slash != NULL) ? strdup(slash + 1) : NULL;
error:
return fname;
}