lvalue required as increment operand

**thagulf2017** · 06-03-2017

i keep experiencing this particular error while doing pointer arithmetics in C/

e.g

Code:

#include <stdio.h>

int strcmp(char *s, char *t);

int main(){

    char s[] = "hello";

    printf("%c", *++s);

}

the error is

C:\Users\xx\Documents\strcmp.c|9|error: lvalue required as increment operand|

but when i changed *++s to *(s+1); it runs and outputs the character 'e'.

are they not essentially the same? as far as i know this works when used for parsing commandline arguments using switch but for an unknown reason barely works normally

**laserlight** · 06-03-2017

Originally Posted by thagulf2017

but when i changed *++s to *(s+1); it runs and outputs the character 'e'.

are they not essentially the same?

No, they are not. *++s pre-increments s, dereferencing the result of the pre-increment. *(s + 1) adds 1 to s, dereferencing the result of the addition. This is the big difference between saying s = s + 1 and saying s + 1. Put it another way: ++s changes s, s + 1 does not. Hence, in your original example, s + 1 is permitted, but ++s is not because s is an array, and arrays cannot be modified (although the content of an array of non-const elements can be modified).

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