Consider the following code:
char str[100];
char str2[100];
strcpy(str, "%alfa% %beta% d%100%d %gamma% %delta%");
printf("printf: ");
printf("1%s2", str);
printf("\nsprintf: ");
sprintf(str2, "1%s2", str); //Interesting stuff happens here
printf(str2);
printf("\n");
The code should format the string "1%s2" by replacing %s with "%alfa%
%beta% d%100%d %gamma% %delta%". First printf is used, and then
sprintf. The output should be:
printf: 1%alfa% %beta% d%100%d %gamma% %delta%2
sprintf: 1%alfa% %beta% d%100%d %gamma% %delta%2
However, this is not what happens i either Visual C++ 6.0, Visual C++
2003 and GCC (version 4 I think, compiled and tested in Linux). In all
these compilers printf works as expected, but fails with sprintf where
the result is either a crash or a malformed string. The problem seems
to be that the %-character is used in the argument which, as fair as I
know, shouldn't be any problem.
If I replace %s with "%%alfa%% %%beta%% d%%100%%d %%gamma%% %%delta%%"
the output will instead by (at least in Visual C++ 2003):
printf: 1%%alfa%% %%beta%% d%%100%%d %%gamma%% %%delta%%2
sprintf: 1%alfa% %beta% d%100%d %gamma% %delta%2
So when using sprintf %% is replaced by % which should be the is these
characters where written in the format string, but this is a very
different case.
Unless I have misunderstand the specification of sprintf there is a
quite critical bug in sprintf and this in several compilers. Is this
an known problem? Are more compilers affected? Why are the problem in
both Visual C++ and GCC? Isn't this very interesting? :-)
PEK
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