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void foo(int x) {
  x = 3; /* persists only lastsuntil untilthe endfunction ofexits function */
  /* ... */
}

Pointers behave in a similar fashion. A function may change a pointer to reference a different object, or NULL, yet that change is discarded once the function exits. Consequently, declaring a pointer as const is unnecessary.

void foo(int *x) {
  x = NULL; /* persists only lastsuntil untilthe endfunction ofexits function */
  /* ... */
}

Noncompliant Code Example

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char *strcat_nc(char *s1, char *s2);

char *str1 = "str1";
const char *str2 = "str2";
char str3[9] = "str3";
const char str4[9] = "str4";

strcat_nc(str3, str2);	/* Compiler warns that str2 is const */
strcat_nc(str1, str3);  /* Attempts to overwrite string literal! */
strcat_nc(str4, str3);  /* Compiler warns that str4 is const */

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In the first strcat_nc() call, the compiler will generate generates a warning about attempting to cast away const on str2. This is a good warning, as because strcat_nc() does not modify its second argument, yet fails to declare it const.

In the second strcat_nc() call, the compiler will happily compile compiles the code with no warnings, but the resulting code will attempt to modify the "str1" literal, which may be impossible; the literal may not be defined in the heap. This violates STR05-C. Use pointers to const when referring to string literals and STR30-C. Do not attempt to modify string literals.

In the final strcat_nc() call, the compiler generates a warning about attempting to cast away const on str4. This is a valid warning.

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char *strcat(char *s1, const char *s2); 

char *str1 = "str1";
const char *str2 = "str2";
char str3[9] = "str3";
const char str4[9] = "str4";

strcat(str3, str2); 

/* Args reversed to prevent overwriting string literal */ 
strcat(str3, str1);  
strcat(str4, str3);  /* Compiler warns that str4 is const */

The const-qualification of the second argument s2 eliminates the spurious warning in the initial invocation, but maintains the valid warning on the final invocation in which a const-qualified object is passed as the first argument (which can change). Finally, the middle strcat() invocation is now valid, as str1 str3 is a valid destination string , as the string exists on the stack and may be safely modified.

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