CERT C: Rec. EXP20-C

Perform explicit tests to determine success, true and false, and equality

Since R2026a

Description

Perform explicit tests to determine success, true and false, and equality¹

Polyspace Implementation

The rule checker checks for Implicit condition check.

Examples

Implicit condition check

Issue

The rule checker reports a violation if a non-boolean value is implicitly compared against TRUE in the condition statement of an if, while, do-while, or ?: (ternary operator) statement. For example:

int x;
//...
if(x){  //implicit condition check
}

Polyspace^® does not report a violation for these cases:

• A Boolean value is compared implicitly against TRUE. For example, this code implicitly compares the Boolean value returned by the function myFunc():

  bool myFunc();
  if(myFunc()){  // No violations
    //.....
  }

  By default, Polyspace considers the bool type defined in stdbool.h as a Boolean type. You can specify additional Boolean types for your code using the option Effective boolean types (-boolean-types).

• A pointer is compared implicitly. For example, this code implicitly compared the pointer ptr:

  int* ptr;
  //...
  if(ptr){  // No violations
  //...
  }

Risk

Using implicit condition check in conditional statements makes your code difficult to maintain and understand. Testing values in your code explicitly makes your code more robust.

Fix

Replace implicit condition checks in your code with explicit tests.

Example

In this example, the header file product.h declares a function validateProduct() that validates the structure Product. The implementation of this function is hidden. In the source file source.c, the function processProducts() expects that validateProduct() return 1 if the validation succeeds, but does not check that the return value is equal to 1 explicitly. Polyspace reports a violation.

• product.h

  #ifndef PRODUCT_H
  #define PRODUCT_H
  
  #include <stdio.h>
  #include <string.h>
  
  #define MAX_NAME_LENGTH 100
  
  typedef struct {
      int id;
      char name[MAX_NAME_LENGTH];
  } Product;
  
  // Function prototype for validating a single Product struct
  int validateProduct(const Product *product);
  
  #endif // PRODUCT_H

• src.c

  #include "product.h"
  
  // Function to process multiple Product structs
  void processProducts(Product *products, size_t count) {
      for (size_t i = 0; i < count; ++i) {
          
          if (validateProduct(&products[i])) {  //Noncompliant
              // Operate on the valid product
              //...
          } else {
             // Handle validation errors
             //...
              
          }
      }
  }
  
  

Correction

To fix this violation, check the returned value of validateProduct() explicitly.

• product.h

  #ifndef PRODUCT_H
  #define PRODUCT_H
  
  #include <stdio.h>
  #include <string.h>
  
  #define MAX_NAME_LENGTH 100
  
  typedef struct {
      int id;
      char name[MAX_NAME_LENGTH];
  } Product;
  
  // Function prototype for validating a single Product struct
  int validateProduct(const Product *product);
  
  #endif // PRODUCT_H

• src.c

  #include "product.h"
  
  // Function to process multiple Product structs
  void processProducts(Product *products, size_t count) {
      for (size_t i = 0; i < count; ++i) {
          
          if (1 == validateProduct(&products[i])) { //Compliant
             // Operate on the valid product
             //...
          } else {
             // Handle validation errors
             //...
              
          }
      }
  }
  
  

Check Information

Group: Rec. 03. Expressions (EXP)

PQL Name: std.cert.EXP20_C

Version History

Introduced in R2026a