Ways to set and get code groups in C programming _c language

C language Setgroups () function: Set Group code function
header file:

 #include <grp.h>

To define a function:

int setgroups (size_t size, const gid_t * list);

Function Description: Setgroups () is used to add the groups indicated in the list array to the group settings of the current process. The gid_t number of the parameter size is list () and the maximum value is Ngroup (32).

Return value: Returns 0 if the setting succeeds, or 1 if there is an error.

Error code:

• Efault: Parameter list array address is not valid.
• Eperm: Insufficient permissions, must be root permission
• Einval: Parameter size value is greater than ngroup (32).

C language GetGroups () function: Getting Group code functions
header file:

#include <unistd.h>  #include <sys/types.h>

To define a function:

int getgroups (int size, gid_t list[]);

Function Description: Getgroup () is used to obtain the group code that the current user belongs to. The parameter size is the number of gid_t that list () can hold. If the parameter size value is zero, this function returns only the number of groups to which the user belongs.

Return value: Returns the group identifier, or returns 1 if there is an error.

Error code:

• Efault: Parameter list array address is not valid.
• Einval: Parameter size value is not sufficient to accommodate all groups.

Example

#include <unistd.h>
#include <sys/types.h>
main ()
{
  gid_t list[500];
  int x, I;
  x = getgroups (0, list);
  GetGroups (x, list);
  for (i = 0; i < x; i++)
    printf ("%d:%d\n", I, List[i]);

Perform:

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