C, C + + difference left value right value

Tag: C + + syntax c differences

C and C + + have some differences in syntax details, although these differences may not be enough to cause differences in the results, some code does have an impact.

This time, the main summary is the difference of the left value right value.

In C, the result of many lvalue operators is no longer an lvalue, whereas in C + +, the result of the lvalue operator is still an lvalue, as long as it is logically feasible. This way of C + + allows for greater flexibility between operator expressions.

1, ++i, we are accustomed to in C + +, I self-added back to myself; however, in c I self-added, the return is a temporary copy, that is, and i++ is the same, this result cannot be an lvalue, that is (++i) = 0 illegal. So I think that's why i++ is used in many for loops in the code, because in C I think i++ is the same as ++i's efficiency.

2, =, similarly, the result in C is the right value, i.e. (a = b) = c is not valid in C, but it is possible in C + +.

3,?:, the branch result returned in C is an rvalue, as stated in C + +, as long as the two branches are lvalue and of the same type, the result is also Lvalue (see, C + + programming language-Special edition section 6.2). This is the following:

{       (1&NBSP;?&NBSP;I=11&NBSP;:&NBSP;J) =22; // c++ The result is i =  22, illegal    printf in C ("%d %d \n",  i, j);       1  ? i=11 : j=22; // c++ result is i = 11, illegal in C, the correct wording is:  1 ? i=11  :  (j=22);    printf ("%d %d \n",  i, j);   //  Thought the result is the same as above, because  ?: Priority is higher than  =, supposedly equivalent to the above expression    //  However, this is the reality, things will never follow your thoughts. The syntax rules in    // c++ are determined   equivalent to:   //  (1)  ?  (i=11)  :  (j =22);   //  See also the C + + programming language-Special edition   section 6.2, such a wonderful expression:   // a =  b < c ? d = e : f = g;  equivalent to:    //  a =  (  (b < c)  ?  (d = e)  :  (f = g)  );   //  This isis the so-called grammar. But it's also quite in line with the programmer's idea. }

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C, C + + difference left value right value