c - Why isn't the compiler generating an error "lvalue required"? -

as per understanding, in line marked 'line 2' of below code, expression (*ptr)++ should generate "lvalue required" error because *ptr evaluates constant value of i=1, not lvalue?

so why program working successfully? or somewhere wrong in concepts? if yes, please enlighten me on this.

int main(void) {     int i;     int *ptr = (int *) malloc(5 * sizeof(int));      (i=0; i<5; i++)         *(ptr + i) = i;      printf("%d ", *ptr++);   //line 1     printf("%d ", (*ptr)++); //line 2      printf("%d ", *ptr);     //line 3     printf("%d ", *++ptr);   //line 4     printf("%d ", ++*ptr);   //line 5 } 

you're having misconception. result of (*ptr) is lvalue, upon post increment operator can applied.

so, in case,

 printf("%d ", (*ptr)++); //line 2 

is fine.

to quote c11 standard, chapter §6.5.3.2, address , indirection operators, ^{(emphasis mine)}

the unary * operator denotes indirection. if operand points function, result function designator; if points object, result lvalue designating object.

fwiw, if *ptr not lvalue, have got error writing *ptr = 5 also, wouldn't it?