CODEWITHSUNDEEP
c++
Jay
Jay

Reputation: 493

std::max - expected an identifier

I'm having a problem with std::max. I can't figure it out.

int border = 35;
int myInt = 2;
int myOtherInt = 3;
int z = std::max(myInt + 2 * border, myOtherInt + 2 * border);

I've included the algorithm standard header. When I mouse over max, I am getting:

Error: expected an identifier

And a compile errors of:

error C2589: '(' : illegal token on right side of '::'
error C2059: syntax error : '::'

What is wrong?

Upvotes: 49

Views: 43651

Answers (6)

starriet 차주녕
starriet 차주녕

Reputation: 3908

Just a brief collection of other answers.

If max(a,b) is already #defined, (by including windows.h or some Windows-related project, etc.)

  1. #define NOMINMAX
  2. #undef max
  3. (std::max) - Use parentheses to prevent function-like macro1)
  4. std::max<int> - Explicitly give a type for the template.

Precaution: If some part of the project depends on the min/max macro, e.g. using MFC, then just simply doing #define NOMINMAX can cause some problem.

Maybe #undef NOMINMAX should be needed, e.g.:

// just an example
#define NOMINMAX
#include <windows.h>
#undef NOMINMAX
// ...

(For more info, please take a look at the answers of this question.)

1) Function-like macros only expand when the next thing after is an opening parenthesis. When surrounding the name with parentheses, the next thing after the name is a closing parenthesis, so no expansion occurs. [ref]

Upvotes: 2

ildjarn
ildjarn

Reputation: 62975

Hazarding a guess, since you're using VC++ – put this before any #includes:

#define NOMINMAX

windows.h defines macros named min and max like so:

#define min(a,b)            (((a) < (b)) ? (a) : (b))
#define max(a,b)            (((a) > (b)) ? (a) : (b))

The Windows SDK has contained these macros since before C++ was standardized, but because they obviously play havoc with the C++ standard library, one can define the NOMINMAX macro to prevent them from being defined.

As a rule, if you're using C++ (as opposed to C) and including windows.h, always define NOMINMAX first.

Upvotes: 93

PeterN
PeterN

Reputation: 29

The "using" declaration (see using Declaration) is yet another way to work around the issue:

int border = 35;
int myInt = 2;
int myOtherInt = 3;
using std::max;
int z = max(myInt + 2 * border, myOtherInt + 2 * border);

It allows using std::max without explicit qualification.

Upvotes: 2

Dave S
Dave S

Reputation: 21058

If you're on VC++, you can either use #define NOMINMAX prior to including any headers, or do (std::max)(myInt + 2 * border, myOtherInt + 2 * border)

Upvotes: 24

jweyrich
jweyrich

Reputation: 32240

Have you tried using ::std::max instead? If this doesn't work, something is messing with your std namespace.

Upvotes: 0

Jim Buck
Jim Buck

Reputation: 20726

I would say that either max is #define's to something else or you need to explicitly invoke the template via std::max<int>.

Upvotes: 4

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