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Alternatively, input character data as a null-terminated byte string and convert to an integer value using strtol() or a related function (see INT06-AC. Use strtol() or a related function to convert a string token to an integer).

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Noncompliant Code Example

This non-compliant noncompliant code example uses the scanf() function to read a string from stdin and convert it to a long. The scanf() and fscanf() functions have undefined behavior if the value of the result of this operation cannot be represented as an integer.

long sl;

if (scanf("%ld", &sl) != 1) {
  /* handler error */
}

Compliant Solution

This compliant example uses fgets() to input a string and strtol() to convert the string to an integer. Error checking is provided to make sure that the value is a valid integer in the range of long.

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Note that this solution treats any trailing characters, including white-space characters, as an error condition.

Risk Assessment

While it is relatively rare for a violation of this rule to result in a security vulnerability, it can easily result in loss or misinterpreted data.

Automated Detection

Fortify SCA Version 5.0 with the CERT C Rule Pack can detect violations of this recommendation.

Related Vulnerabilities

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

References

\[[Klein 02|AA. C References#Klein 02]\]
\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.20.1.4, "The strtol, strtoll, strtoul, and strtoull functions," and Section 7.19.6, "Formatted input/output functions"

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INT04-C. Enforce limits on integer values originating from untrusted sources      04. Integers (INT)       INT06-AC. Use strtol() or a related function to convert a string token to an integer