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The solution is to provide the open and close parentheses following the geteuid token so that the function is properly invoked.:

/* First the options that are only allowed for root */
if (getuid() == 0 || geteuid() != 0) {
  /* ... */
}

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A function pointer can be compared to a null function pointer of the same type.:

/* First the options that are only allowed for root */ 
if (getuid == (uid_t(*)(void))0 || geteuid != (uid_t(*)(void))0) { 
  /* ... */ 
} 

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In this noncompliant code example, the function pointer do_xyz is implicitly compared unequal to 0.:

int do_xyz(void); 
 
if (do_xyz) { 
  /* handle error */ 
} 

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In this compliant solution, the function do_xyz() is invoked and the return value is compared to 0.:

int do_xyz(void); 
 
if (do_xyz()) { 
  /* handle error */ 
} 

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