# V618. Dangerous call of 'Foo' function. The passed line may contain format specification. Example of safe code: printf("%s", str);

The analyzer has detected that a formatted output function call might cause an incorrect result. Moreover, such a code can be used for an attack (see this article for details).

The string is output directly without using the "%s" specifier. As a result, if there is a command character added into the string accidentally or deliberately, it will cause a program failure. Consider a simplest example:

    char *p;
    ...
    printf(p);

The call of the printf(p) function is incorrect, as there is no format string of the "%s" kind. If there are format specifications to be found in the 'p' string, this output will be most likely incorrect. The following code is safe:

    char *p;
    ...
    printf ("%s", p);

The V618 warning might seem insignificant. But actually this is a very important thing when creating quality and safe programs.

Keep in mind that you may come across format specifications (%i, %p and so on) in a string quite unexpectedly. It may occur accidentally when user inputs incorrect data. It may also occur deliberately when incorrect data are input consciously. Absence of the "%s" specifier may cause program crash or output of private data somewhere outside the program. Before you turn off the V618 diagnostic, we insist that you read the article "Wade not in unknown waters. Part two". Corrections to the code you'll have to make will be too few to ignore this type of defects.

Note. The analyzer tries not to generate the V618 warning when a function call cannot have any bad consequences. Here is an example when the analyzer won't show you the warning:

    printf("Hello!");

This diagnostic is classified as:

CWE-134 CERT-FIO30-C

You can look at examples of errors detected by the V618 diagnostic.