FMTCHECK(3) BSD Library Functions Manual FMTCHECK(3)NAME
fmtcheck -- sanitizes user-supplied printf(3)-style format string
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
const char *
fmtcheck(const char *fmt_suspect, const char *fmt_default);
DESCRIPTION
The fmtcheck function scans fmt_suspect and fmt_default to determine if fmt_suspect will consume the same argument types as fmt_default and
to ensure that fmt_suspect is a valid format string.
The printf(3) family of functions can not verify the types of arguments that they are passed at run-time. In some cases, like catgets(3), it
is useful or necessary to use a user-supplied format string with no guarantee that the format string matches the specified parameters.
The fmtcheck function was designed to be used in these cases, as in:
printf(fmtcheck(user_format, standard_format), arg1, arg2);
In the check, field widths, fillers, precisions, etc. are ignored (unless the field width or precision is an asterisk '*' instead of a digit
string). Also, any text other than the format specifiers is completely ignored.
Note that the formats may be quite different as long as they accept the same parameters. For example, "%p %o %30s %#llx %-10.*e %n" is com-
patible with "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)." However, "%o" is not equivalent to "%lx" because the
first requires an integer and the second requires a long.
RETURN VALUES
If fmt_suspect is a valid format and consumes the same argument types as fmt_default, then the fmtcheck function will return fmt_suspect.
Otherwise, it will return fmt_default.
SEE ALSO printf(3)BSD October 17, 2000 BSD
Check Out this Related Man Page
FMTCHECK(3) BSD Library Functions Manual FMTCHECK(3)NAME
fmtcheck -- sanitizes user-supplied printf(3)-style format string
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
const char *
fmtcheck(const char *fmt_suspect, const char *fmt_default);
DESCRIPTION
The fmtcheck() scans fmt_suspect and fmt_default to determine if fmt_suspect will consume the same argument types as fmt_default and to
ensure that fmt_suspect is a valid format string.
The printf(3) family of functions cannot verify the types of arguments that they are passed at run-time. In some cases, like catgets(3), it
is useful or necessary to use a user-supplied format string with no guarantee that the format string matches the specified arguments.
The fmtcheck() was designed to be used in these cases, as in:
printf(fmtcheck(user_format, standard_format), arg1, arg2);
In the check, field widths, fillers, precisions, etc. are ignored (unless the field width or precision is an asterisk '*' instead of a digit
string). Also, any text other than the format specifiers is completely ignored.
RETURN VALUES
If fmt_suspect is a valid format and consumes the same argument types as fmt_default, then the fmtcheck() will return fmt_suspect. Other-
wise, it will return fmt_default.
SECURITY CONSIDERATIONS
Note that the formats may be quite different as long as they accept the same arguments. For example, "%p %o %30s %#llx %-10.*e %n" is com-
patible with "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)". However, "%o" is not equivalent to "%lx" because the
first requires an integer and the second requires a long.
SEE ALSO printf(3)BUGS
The fmtcheck() function does not recognize positional parameters.
BSD October 16, 2002 BSD
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