Using the following code produces different results in 5.6.1 and 5.8.0 (compiled with the same compiler version and the same flags except that 5.8.0 was compiled with ithreads): 
# file: printf.pl
printf "%4.4f\n",   3.14159;
printf "%4.4lf\n",  3.14159;
printf "%4.4hf\n",  3.14159;
printf "%4.4qf\n",  3.14159;
printf "%4.4Lf\n",  3.14159;
printf "%4.4llf\n", 3.14159;

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Results: 

$ /usr/bin/perl5.6.1 printf.pl 
3.1416
3.1416
3.1416
%4.4qf
%4.4Lf
%4.4llf

$ /usr/local/bin/perl5.8.0 printf.pl 
3.1416
%4.4lf
%4.4hf
%4.4qf
3.1416
3.1416

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As it turns out, none of these printf size flags are tested in either 5.6.1 or 5.8.0 core tests. The relevant config details for each version are the same (snipped for brevity): 

Summary of my perl5 (revision 5.0 version 6 subversion 1) configuratio
+n:
    use64bitint=undef use64bitall=undef uselongdouble=undef

    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=4, usemymalloc=n, prototype=define


Summary of my perl5 (revision 5.0 version 8 subversion 0) configuratio
+n:
    use64bitint=undef use64bitall=undef uselongdouble=undef

    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=4, prototype=define

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This was noticed when installing Text::Reform with 5.8.0, the module has a single case of using sprintf with an 'lf' (at line 141) which passes all tests on my 5.6.1 but fails on my 5.8.0. My questions: is it at all wise to use these size flags? Is this a perl bug not detected because it isn't tested for? Shouldn't the size flags (l,h,q,L,and ll) simply be ignored if unsupported on a given platform? (platform is linux)

In reply to printf size flag incompatibility by Anonymous Monk

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