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At compile time, string literals are used to create an array of static duration and sufficient length to contain the character sequence and a null-termination character. It is unspecified wehether these arrays are distinct. The behavior is undefined if a program attempts to modify string literals but frequently results in an access violation as string literals are typically stored in read-only memory.

Non-compliant Code Example

Do not attempt to modify a string literal. In the following example, the char pointer p is initialized to the address of the static string. Attempting to modify the string literal result results in undefined behavior.

char *p  = "string literal";
p[0] = 'S';

Compliant Solution

As an array initializer, a string literal specifies the initial values of characters in an array (as well as the size of the array). The following code creates a copy of the string literal in the space allocated to the character array a. The string stored in a can be safely modified.

char a[] = "string literal";
a[0] = 'S';

Consequences

Abnormal program termination.
Denial-of-service attack.

References

• ISO/IEC 9899-1999 Section 6.4.5 String literals
• Summit 95 comp.lang.c FAQ list - Question 1.32