DCL01-A. Do not reuse variable names in sub-scopes

Do not use the same variable name in two scopes where one scope is contained in another. Examples include:

• No other variable should share the name of a global variable if the other value is in a subscope of the global variable.
• A block should not declare a variable with the same name as a variable declared in any block that contains it.

Reusing variable names leads to programmer confusion about which variable is being modified. Additionally, if variable names are reused, generally one or both of the variable names are too generic.

Non-Compliant Code Example

In this example, the programmer sets the value of the msg variable, expecting to reuse it outside the block. Due to the reuse of the variable name, however, the outside msg variable value is not changed.

char msg[100];

void hello_message() {
  char msg[80] = "Hello";
  strcpy(msg, "Error");
}

Compliant Solution

This compliant solution uses different, more descriptive variable names.

char error_msg[100];

void hello_message() {
  char hello_msg[80] = "Hello";
  strcpy(error_msg, "Error");
}

When the block is small, the danger of reusing variable names is mitigated by the visibility of the immediate declaration. Even in this case, however, variable name reuse is not desirable.

Risk Assessment

Reusing a variable name in a sub-scope can lead to unintended values for the variable.

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[ISO/IEC 9899-1999]] Section 5.2.4.1, "Translation limits"
[[MISRA 04]] Rule 5.2

DCL00-A. Declare immutable values using enum or const      02. Declarations and Initialization (DCL)       DCL02-A. Use visually distinct identifiers