MISRA C:2012 Rule 15.5

A function should have a single point of exit at the end

Description

Rule Definition

A function should have a single point of exit at the end¹ .

Rationale

This rule requires that a return statement must occur as the last statement in the function body. Otherwise, the following issues can occur:

• Code following a return statement can be unintentionally omitted.

• If a function that modifies some of its arguments has early return statements, when reading the code, it is not immediately clear which modifications actually occur.

Troubleshooting

If you expect a rule violation but do not see it, refer to Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

More Than One return Statement in Function

#define MAX ((unsigned int)2147483647)
#define NULL (void*)0

typedef unsigned int bool_t;
bool_t false = 0;
bool_t true = 1;

bool_t f1(unsigned short n, char *p) {          /* Non-compliant */
    if(n > MAX) {
        return false;
    }

    if(p == NULL) {
        return false;
    }

    return true;
}

In this example, the rule is violated because there are three return statements.

Correction — Use Variable to Store Return Value

One possible correction is to store the return value in a variable and return this variable just before the function ends.

#define MAX ((unsigned int)2147483647)
#define NULL (void*)0

typedef unsigned int bool_t;
bool_t false = 0;
bool_t true = 1;
bool_t return_value;

bool_t f2 (unsigned short n, char *p) {         /* Compliant */
    return_value = true;
    if(n > MAX) {
        return_value = false;
    }

    if(p == NULL) {
        return_value = false;
    }

    return return_value;
}

Check Information

Group: Control Flow

Category: Advisory

AGC Category: Advisory

Version History

Introduced in R2014b

R2024b: return statement as the last line of a do-while statement

Polyspace^® does not report a violation of this rule when a return statement is the last line of the do portion of a do-while statement. For example:

uint8_t exampleA(void) {
     do {
          uint8_t a;
          a = get_uint8();
          return(a);            //Compliant
     }
     while (0);
}