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How to specify additional code information by using _Analysis_assume_

  • Artikkeli

You can provide hints to the code analysis tool for C/C++ code that help the analysis process and reduce warnings. To provide additional information, use the following function macro:

_Analysis_assume_( expr )

expr - any expression that is assumed to evaluate to true.

The code analysis tool assumes that the condition represented by the expression expr is true at the point where the function appears. And, it remains true until expr is altered, for example, by assignment to a variable.

Note

_Analysis_assume_ does not impact code optimization. Outside the code analysis tool, _Analysis_assume_ is defined as a no-op.

Example

The following code uses _Analysis_assume_ to correct the code analysis warning C6388:

#include <windows.h>
#include <sal.h>

// Requires pc to be null.
void f(_Pre_null_ char* pc);

// Calls free and sets ch to null.
void FreeAndNull(char** ch);

void test()
{
    char* pc = (char*)malloc(5);
    FreeAndNull(&pc);
    _Analysis_assume_(pc == NULL);
    f(pc);
}

_Analysis_assume_ should be used as a last resort. We should first try to make the contracts of the functions more precise. In this case we could improve the contract of FreeAndNull instead of using _Analysis_assume_:

#include <windows.h>
#include <sal.h>

// Requires pc to be null.
void f(_Pre_null_ char* pc);

// Calls free and sets ch to null.
_At_(*ch, _Post_null_)
void FreeAndNull(char** ch);

void test()
{
    char* pc = (char*)malloc(5);
    FreeAndNull(&pc);
    f(pc);
}

See also