Static code checking finds the following types of errors:
This section describes possible causes of the error and a code example of when the error might occur.
Possible causes: Attempting to read memory beyond the array bounds.
Example:
int a[5];
. . .
printf("a[5] = %d\n",a[5]); // Reading memory beyond array bounds
Possible causes: Attempting to write memory beyond the array bounds.
Example:
int a [5];
. . .
a[5] = 5; // Writing to memory beyond array bounds
Possible Causes: Calling free()() more than once with the same pointer. In C++, using the delete operator more than once on the same pointer.
Example:
int *p = (int*) malloc(sizeof(int));
free(p);
. . . // p was not signed a new value between the free statements
free(p); // Double freeing memory
Possible Causes: The explicit type cast might violate aliasing rules at alias level higher than "any".
Example:
#include<stdio.h>
int i =2;
int *pi =&i;
short *ps;
int foo()
{
ps=(short*)pi; // type cast violation
*ps=1;
return (*pi);
}
void main()
{
printf("%d",foo());
}
Example:
int *p = (int*) malloc(sizeof(int));
free(p);
. . . // Nothing assigned to p in between
printf("p = 0x%h\n", *p); // Reading from freed memory
Example:
int *p = (int*) malloc(sizeof(int));
free(p);
. . . // Nothing assigned to p in between
*p = 1; // Writing to freed memory
Example:
int x=0;
int i=0;
while (i200) {
x++; } // Infinite loop
Possible causes: Memory is allocated but not freed before exit or escaping from the function.
Example:
int foo()
{
int *p = (int*) malloc(sizeof(int));
if (x) {
p = (int *) malloc(5*sizeof(int)); // will cause a leak of the 1st malloc
}
} // The 2nd malloc leaked here
Possible causes: Missing return values along some paths to exit.
Example:
#include <stdio.h>
int foo (int a, int b)
{
if (a)
{
return b;
}
} // If foo returns here, the return is uninitialized
int main ( )
{
printf("%d\n", foo(0,30));
}
Possible causes: Accessing a return value from malloc in C or a new operator in C++ without checking against null.
Example:
#include <stdlib.h>
int main()
{
int *p3 = (int*) malloc(sizeof(int)); // Missing null-pointer check after malloc.
*p3 = 0;
}
Possible causes: Code is returning an uninitialized value.
Example:
foo() <nfr.c : 7>
4: int foo()
5: {
6: int i;
7:=> return i;
8: }
Possible causes: Accessing a pointer that might equal to null, or redundant checking against null in case the pointer is never null.
Example:
#include <stdio.h>
#include <stdlib.h>
int gp, ctl;
int main()
{
int *p = gp;
if (ctl)
p = 0;
printf ("%c\n", *p); // May be null pointer dereference
if (!p)
*p = 0; // Surely null pointer dereference
int *p2 = gp;
*p2 = 0; // Access before checking against NULL.
assert (p2!=0);
int *p3 = gp;
if (p3) {
printf ("p3 is not zero.\n");
}
*p3 = 0; // Access is not protected by previous check against NULL.
}
Example:
#include <stdlib.h>
int *foo ()
{
int *p = (int*) malloc(sizeof(int));
free(p);
return p; // Return freed memory is dangerous
}
int main()
{
int *p = foo();
*p = 0;
}
Possible causes: Reading local or heap data that has not been initialized.
Example:
#include <stdio.h>
#include <stdlib.h>
struct ttt {
int a: 1;
int b: 1;
};
int main()
{
int *p = (int*) malloc(sizeof(int));
printf("*p = %d\n",*p); // Accessing uninitialized data
struct ttt t;
extern void foo (struct ttt *);
t.a = 1;
foo (&t); // Access uninitialized bitfield data "t.b"
}
Possible causes: Reading local or heap data that has not been initialized.
Example:
int foo();
int main()
{
foo(); // Return value is not used.
}
Possible causes: Reading local or heap data that has not been initialized.
Example:
int main()
{
int *p = (int *)0;
void bar (int *);
{
int a[10];
p = a;
} // local variable 'a' leaked out
bar(p);
}