int a=5; ++a=a; Please find the above code segment. The code is ok for the c++(g++) compiler but shows error while using c (gcc) compiler. May I know the reason for this? The error in c compiler is "lvalue required as left operand of assignment".
- In C ++a refers to a value not a variable not sure about C++bikram990– bikram9902013-05-09 05:29:54 +00:00Commented May 9, 2013 at 5:29
- Related: stackoverflow.com/questions/3690141/…user529758– user5297582013-05-09 05:30:23 +00:00Commented May 9, 2013 at 5:30
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2 Answers
There is operator overloading in C++ (and you can overload pre-increment also), so to achieve some additional goals pre-increment operator returns lvalue in C++.
For example:
Your class may implement some pointer functionality and may need:
- pre-increment for pointer shifting;
- assignment operator for assignment to pointer value (value by the address).
Pre-increment may be useful in this case.
Abstract code example:
class MyIntPtr { int *val; ... public: MyIntPtr(int *p) { ... }; MyIntPtr &operator++() { ++val; return *this; }; void operator=(int i) { *val = i; } ... }; ... int array[10]; MyIntPtr ptr(array); for(int i = 0; i < sizeof array; ++i) ++ptr = i; 
Comments
Because in C++, the preincrement operator yields an lvalue, whereas in C, it's an rvalue.
4 Comments
akhil
"In C++, the preincrement operator yields an lvalue, whereas in C, it's an rvalue ".Why it is so?
akhil
May i know what is internally happening in both compiler. Is there any valid documentation?
@akhil There's the C++11 standard from which you can select the right pieces of information. What do you mean by "what happens internally in the compiler"? It parses the source text and outputs machine code, that's what happens.