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String literals are constant and should only be assigned to constant pointers. This recommendation supports rule STR30-C.

Non-Compliant Code Example

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The const keyword is not included in this declaration.

Code Block
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char *c = "Hello"; /* Bad: assigned to non-const */ c[3] = 'a'; /* Undefined (but compiles) */

Compliant Solution 1

The compiler will not allow In cases where the string referenced by c is not meant to be modified, c should be declared as a const pointers,
preventing direct manipulation of the contents of the string literals that are assignhed to const pointers.

char const *c = "Hello"; /* Good */
//c[3] = 'a'; would cause a compile error

Aside

Compliant Solution 1

In cases where the string referenced by c is meant to be modified, use initialization instead of assignment. In this compliant solution, both a and b are modifiable char arrays which have been initialized using the contents of the corresponding string literalNote that the following code is acceptable, as a and b do not actually point to string literals. They are char array objects which have had characters copied into them, and therefore are modifiable.

char a[] = "abc";
char b[3] = "abc";

The above code is equivalent to:

char a[] = {'a', 'b', 'c', '\0'};
char b[] = {'a', 'b', 'c'};

Non-Compliant

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Code Example

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1

Though it is not compliant with the C Standard, this code executes correctly if the contents of CMUfullname are not modified.

char *CMUfullname = "Carnegie Mellon";

/* get school from user input and validate */

if (strcmp(school,"CMU")) {
    school = CMUfullname;
}

Non-Compliant

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Code Example 2

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Adding in the const keyword will generate a compiler warning, as the assignment of CMUfullname to school discards the const qualifier. Any modifications to the contents of school after this assignment will lead to errors.

Code Block
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char const *CMUfullname = "Carnegie Mellon"; /* get school from user input and validate */ if (strcmp(school,"CMU")) { school = CMUfullname; }

Compliant Solution

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The compliant solution uses the const keyword to protect the string literal, as well as using strcpy() to copy the value of CMUfullname into school, allowing future modification of school.

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