Topic: functions in C

Question

How can we identify whether a function is call by value or call by refrence?? 

by looking at the defination or by looking at the statement where it is called.

please someone explain

Comments

C has only call by value.

Answer 1

Actually in C, only call by value is possible

In GATE, they give the question with call by value but they can say what happened if it is call by reference. then simply u can assume like it is a global variable.

void change(int a,int b)

{

     int temp=a;

     a=b;

     b=temp;

}

int main()

{

       int i1=10,i2=20;

      swap(i1,i2);

      printf("i1 = %d, i2 = %d \n");

}

o/p :-  i1=10,i2=20 ------------ by default, as per C, call by value

o/p :- i1=20,i2=10 -----------  if they specified call by reference

 

Credit to @ Arjun sir

Comments

Whatever you pass as argument in C be it value or address are copied to formal parameters - so these are call by value only.

---

func1(char* s1, char* s2){
    char* temp;
    temp = s1;
    s1 = s2;
    s2 = temp;
}

so that means this function is called by reference, if i make a call like

func1(&s1,&s2);

and it can swap the actual prameters.???

---

No, saif it's not call by reference.... it is also call by value

in this case just addresses are copied into the s1 and s2

---

True

See,When one is sending address & receiving through pointers, one is sending the value only.

but when one is sending or receiving a reference variable, one is sending an alias

i.e another name of the variable which is exactly Call by  reference.It means formal parameter itself act as alias of actual parameter and If we will perform any operation on alias our actual parameter will change and C doesn't Support this feature.

---

#include<stdio.h>
void fun1(char *s1, char *s2){
char *tmp;
tmp = s1;
s1 = s2;
s2 = tmp;
}
void fun2(char **s1, char **s2){
char *tmp;
tmp = *s1;
*s1 = *s2;
*s2 = tmp;
}
int main(){
char *str1 = "Hi", *str2 = "Bye";
fun1(str1, str2); printf("%s %s ", str1, str2);
fun2(&str1, &str2); printf("%s %s", str1, str2);
return 0;
}

 

 

 

But sir according to the question asked in gate 2018 the fun2 is actually swapping the actual parameters. Why if C does not support call by reference.

Please explain this

---

It is done via '*' operator which gets the value from the passed address. But this is not the actual or formal parameter - actual parameter is the address location. You cannot find any standard resource which says C supports pass by reference but you can find plenty of weblinks because any jobless person can create one.

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like global vars or passing pointers