c++ - conversion to static_cast<unsigned char> -


does conversion like:

int a[3]; char i=1; a[ static_cast<unsigned char>(i) ];

introduce overhead conversions or can compiler optimize away? interested because want rid of -wchar-subscripts warnings, want use char index (other reasons)

i did 1 test on clang 3.4.1 code :

int ival(signed char c) {     int a[] = {0,1,2,3,4,5,6,7,8,9};     unsigned char u = static_cast<unsigned char>(c);     return a[u]; }

here relevant part or assembly file generated c++ -s -o3 

_z4ivala:                               # @_z4ivala # bb#0:     pushl   %ebp     movl    %esp, %ebp     movzbl  8(%ebp), %eax     movl    .l_zz4ivalae1a(,%eax,4), %eax     popl    %ebp     ret

there no trace of conversion.


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