Operand Must Be A Modifiable Lvalue Error
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Expression Must Be A Modifiable Lvalue In C++
Overflow the company Business Learn more about hiring developers or posting ads with us expression must be a modifiable lvalue c Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a expression must be a modifiable lvalue char array community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Expression must be a modifiable L-value up vote 15 down vote favorite 8 I have
Expression Must Be A Modifiable Lvalue Array
here char text[60]; Then I do in an if: if(number == 2) text = "awesome"; else text = "you fail"; and it always said expression must be a modifiable L-value. c char variable-assignment lvalue share|improve this question edited Feb 15 at 20:16 tuple_cat 21.8k52868 asked May 15 '11 at 13:41 Mysterigs 83118 add a comment| 1 Answer 1 active oldest votes up vote 24 down vote accepted You cannot change the
Expression Must Be A Modifiable Lvalue Struct
value of text since it is an array, not a pointer. Either declare it as char pointer (in this case it's better to declare it as const char*): const char *text; if(number == 2) text = "awesome"; else text = "you fail"; Or use strcpy: char text[60]; if(number == 2) strcpy(text, "awesome"); else strcpy(text, "you fail"); share|improve this answer answered May 15 '11 at 13:45 MByD 98.3k17185215 Omg i am a noob :(. Thank you ! it works :D –Mysterigs May 15 '11 at 13:47 14 :). lvalue means the left value (should be assignable) –MByD May 15 '11 at 13:48 add a comment| Your Answer draft saved draft discarded Sign up or log in Sign up using Google Sign up using Facebook Sign up using Email and Password Post as a guest Name Email Post as a guest Name Email discard By posting your answer, you agree to the privacy policy and terms of service. Not the answer you're looking for? Browse other questions tagged c char variable-assignment lvalue or ask your own question. asked 5 years ago viewed 46685 times active 8 months ago Linked 1 Trouble placing int matrix array in a C++ Object -1 No instance of overloaded function matches argument list. Re
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers or posting ads expression must be a modifiable lvalue in c struct with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the
Expression Must Be A Modifiable Lvalue Const
Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: expression must be a modifiable lvalue pointer Sign up Expression must be a modifiable lvalue up vote 3 down vote favorite I have this following code: int M = 3; int C = 5; int match = 3; for ( int k =0; k < C; k ++ http://stackoverflow.com/questions/6008733/expression-must-be-a-modifiable-l-value ) { match --; if ( match == 0 && k = M ) { std::cout << " equals" << std::endl; } } But it gives out an error saying: Error: expression must be a modifiable value on that "if" line. I am not trying to modify "match" or "k" value here, but why this error? if I only write it like: if ( match == 0 ) it is ok. Could someone explain it to me? c++ if-statement share|improve this question edited http://stackoverflow.com/questions/12745601/expression-must-be-a-modifiable-lvalue Nov 20 '15 at 20:39 Brian Tompsett - 汤莱恩 3,101132775 asked Oct 5 '12 at 11:45 E_learner 901102961 6 Did you mean k == M? –Kerrek SB Oct 5 '12 at 11:47 1 K == M not K = M –Shashwat Oct 5 '12 at 11:48 1 You're lucky that it resulted in a compiler error due to the operator precedences of && and =, instead of silently producing an incorrect program! –Rufflewind Aug 24 '14 at 1:47 add a comment| 4 Answers 4 active oldest votes up vote 19 down vote accepted The assignment operator has lower precedence than &&, so your condition is equivalent to: if ((match == 0 && k) = m) But the left-hand side of this is an rvalue, namely the boolean resulting from the evaluation of the subexpression match == 0 && k, so you cannot assign to it. By contrast, comparison has higher precedence, so match == 0 && k == m is equivalent to: if ((match == 0) && (k == m)) share|improve this answer answered Oct 5 '12 at 11:49 Kerrek SB 285k40519753 add a comment| up vote 4 down vote In C, you will also experience the same error if you declare a: char array[size]; and than try to assign a value without specifying an index position: array = '\0'; By doing: array[index] = '0\'; You're specifying the accessible/modifiable address previously declared. share|improve this answer answered Apr 17 '15 at 14:20 Alan 330
evaluate expressions, you'd better develop a taste. An expression is a sequence of operators and operands that specifies a computation. That computation might produce a resulting value and it might generate side effects. An assignment expression has the form: e1 = e2 where e1 and e2 are themselves expressions. The right operand e2 can be any expression, http://ieng9.ucsd.edu/~cs30x/Non-modifiable%20Lvalues.htm but the left operand e1 must be an lvalue expression. That is, it must be an expression http://www.ibm.com/support/docview.wss?uid=isg1PM43942 that refers to an object. As I explained last month ("Lvalues and Rvalues," June 2001, p. 70), the "l" in lvalue stands for "left," as in "the left side of an assignment expression." For example: int n; declares n as an object of type int. When you use n in an assignment expression such as: n = 3; the n is an expression (a subexpression of the must be assignment expression) referring to an int object. The expression n is an lvalue. On the other hand: 3 = n; causes a compilation error, and well it should, because it's trying to change the value of an integer constant. Although the assignment's left operand 3 is an expression, it's not an lvalue. It's an rvalue. An rvalue is simply any expression that is not an lvalue. It doesn't refer to an object; it just represents a value. Although lvalue gets its name from the kind must be a of expression that must appear to the left of an assignment operator, that's not really how Kernighan and Ritchie defined it. In the first edition of The C Programming Language (Prentice-Hall, 1978), they defined an lvalue as "an expression referring to an object." At that time, the set of expressions referring to objects was exactly the same as the set of expressions eligible to appear to the left of an assignment operator. But that was before the const qualifier became part of C and C++. The const qualifier renders the basic notion of lvalues inadequate to describe the semantics of expressions. We need to be able to distinguish between different kinds of lvalues. And that's what I'm about to show you how to do. But first, let me recap. A few key points The assignment operator is not the only operator that requires an lvalue as an operand. The unary & (address-of) operator requires an lvalue as its sole operand. That is, &n is a valid expression only if n is an lvalue. Thus, an expression such as &3 is an error. The literal 3 does not refer to an object, so it's not addressable. Not only is every operand either an lvalue or an rvalue, but every operator yields either an lvalue or an rvalue as its result. For example, the binary + operator yields an rvalue. Given integer objects m and n: m + 1 = n; is an error. The + operator has higher precedence than the =
CORRECTCODE IN TESTCASE AND SHOULD NOT BE FLAGGED AS ERRORS. VSE/ESA A fix is available Obtain the fix for this APAR. Subscribe You can track all active APARs for this component. APAR status Closed as program error. Error description Errors labeled 'Operand must be a modifiable lvalue.' in testcase are valid code and should not be flagged as errors. Local fix Problem summary **************************************************************** * USERS AFFECTED: All users of the C/VSE compiler * **************************************************************** * PROBLEM DESCRIPTION: Valid code gives error EDC0127 * * 'If the operands are pointers, they * * must point to compatible types.' Even * * when types are compatible OR error * * EDC0114: 'Operand must be amodifiable * * lvalue.' even when the lvalue is * * modifiable. * **************************************************************** * RECOMMENDATION: * **************************************************************** This is a front end fix sysrouted from APAR PQ02052. Integer pointers should be able to point to addresses stored by a constant integer pointer. The following code that was generating errors now runs as expected: int *const p; int *p1; *p = 1234 p1 = &p 3 ; //Should not cause errors Also, a const pointer to an array should be modifiable as below int a 2 ; int * const p = a; void func() p 1 = 1; // should be okay Problem conclusion The error is no longer issued and pointers are handled correctly by the C/VSE compiler. Temporary fix Comments APAR Information APAR numberPM43942 Reported component nameC/VSE COMPILER Reported component ID5686A0100 Reported release1FY StatusCLOSED PER PENoPE HIPERNoHIPER Special AttentionNoSpecatt Submitted date2011-07-19 Closed date2011-07-26 Last modified date2011-11-04 APAR is sysrouted FROM one or more of the following: PQ02052 APAR is sysrouted TO one or more of th