LANG.STRUCT.UC : Unreachable Code: 5 warning classes

Some of the code in a function is not reachable from the function entry point under any circumstances.

The following table lists the available unreachable code warning classes in order of severity, with the most severe ("Unreachable Call") first. The warning class associated with a block of unreachable code will be the most severe class that is applicable to the statements in the block.

Warning Class Name	Most Serious Statement Type in Unreachable Set
Unreachable Call	A call site.
Unreachable Computation	A statement that performs computation (such as addition) on data.
Unreachable Conditional	A branch statement, such as if, while, switch, ?, &&,\|\|.
Unreachable Data Flow	A simple assignment, or a return statement with a value.
Unreachable Control Flow	A non-branching statement that influences control flow, such as break, goto, continue, or return with no value.

Properties

WARNING_FILTER += allow categories:LANG.STRUCT.UC
WARNING_FILTER += discard categories:LANG.STRUCT.UC

Example

#include <stdlib.h>
#include <stddef.h>

void g(void);

int f(int i){
    if( i ) exit( i );
    return 0;
}

/* For unreachable_computation(), unreachable_conditional(),
 * unreachable_conditional(), and unreachable_data_flow(), the first
 * statement in the function body is
 *    int rv = f(5);
 *
 * The call to f() is reachable but never returns, so the remainder of
 * the function, including the assignment of the return value to rv
 * that takes place in the same statement, is unreachable. (This
 * assignment is itself a data flow.) The warning class for each of
 * these cases will depend on the nature of the statements in the
 * unreachable block.
 */
int unreachable_call(int x){
    int p;
    int rv = f(5); /* 'Unreachable Call' warning issued here */
    g();                       /* call (highest severity) */
    rv += x;                   /* computation */
    if (x>5) {                 /* conditional */ 
      return 0;                /* data flow */
    }
    p = rv;                    /* data flow */
    return p;
}

int unreachable_computation(int x){
    int p;
    int rv = f(5); /* 'Unreachable Computation' warning issued here */
    rv += x;                   /* computation (highest severity) */   
    if (x>5) {                 /* conditional */ 
      return 0;                /* data flow */
    }
    p = rv;                    /* data flow */
    return p;
}

int unreachable_conditional(int x){
    int p;
    int rv = f(5); /* 'Unreachable Conditional' warning issued here */ 
    if (x>5) {                 /* conditional (highest severity) */ 
      return 0;                /* data flow */
    }
    p = rv;                    /* data flow */
    return p;
}

int unreachable_data_flow(){
   int p;
   int rv = f(5);  /* 'Unreachable Data Flow' warning issued here */
   p = rv;                    /* data flow */
   return p;
}


/* In unreachable_control_flow(), a return statement is unreachable
 * because it is in the TRUE branch of an IF statement whose condition
 * always evaluates to FALSE.
 */
void unreachable_control_flow(int x, int y){
    char *q = NULL;
    while (q==NULL){
       q = (char *) malloc(5 * sizeof(char));
    }
    if (q==NULL) {                       /* ('Redundant Condition' warning issued here) */
        return;    /* 'Unreachable Control Flow' warning issued here */
    }
    free(q);
}

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.

LANG.STRUCT.UC : Unreachable Code: 5 warning classes

Summary

Properties

Example

Relevant Configuration File Parameters