Problem - Kevin Tafuro

The function used to look up user information by name has the following signature:
#include
#include
struct passwd *getpwnam(const char *name);
Both functions return a pointer to a structure allocated internally by the runtime
library. One side effect of this behavior is that successive calls replace the information
from the previous call. Another is that the functions are not thread-safe. If either
function fails to find the requested user information, a NULL pointer is returned.
The contents of the passwd structure differ across platforms, but some fields remain
the same everywhere. Of particular interest to us in this recipe are the two fields pw_
name and pw_uid. These two fields are what enable mapping between names and
numeric identifiers. For example, the following two functions will obtain mappings:
#include
#include
#include
int spc_user_getname(uid_t uid, char **name) {
struct passwd *pw;
if (!(pw = getpwuid(uid)) ) {
endpwent( );
return -1;
}
*name = strdup(pw->pw_name);
endpwent( );
return 0;
}
int spc_user_getuid(char *name, uid_t *uid) {
struct passwd *pw;
if (!(pw = getpwnam(name))) {
endpwent( );
return -1;
}
*uid = pw->pw_uid;
endpwent( );
return 0;
}
Note that spc_user_getname( ) will dynamically allocate a buffer to return the user’s
name, which must be freed by the caller. Also notice the use of the function
endpwent( ). This function frees any resources allocated by the lookup functions. Its
use is important because failure to free the resources can cause unexpected leaking of
memory, file descriptors, socket descriptors, and so on. Exactly what types of
resources may be leaked vary depending on the underlying implementation, which
may differ not only from platform to platform, but also from installation to installation.
Getting User and Group Information on Unix | 373
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