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copied!<p>Because the C(99) standard requires (§6.5.3.4/1)</p> <blockquote> <p><strong>The <code>sizeof</code> operator shall not be applied to an expression that has function type</strong> or an incomplete type, to the parenthesized name of such a type, or to an expression that designates a bit-field member. </p> </blockquote> <p>so the return value is meaningless. If you need the <code>sizeof</code> the function pointer, use </p> <pre><code>sizeof(&main) sizeof(&printf) sizeof(&scanf) </code></pre> <hr> <p>gcc returns 1 on types that the sizeof is meaningless (see <a href="http://gcc.gnu.org/viewcvs/trunk/gcc/c-family/c-common.c?revision=164754&view=markup" rel="noreferrer">c-common.c</a>):</p> <pre><code>4187 if (type_code == FUNCTION_TYPE) 4188 { 4189 if (is_sizeof) 4190 { 4191 if (complain && (pedantic || warn_pointer_arith)) 4192 pedwarn (loc, pedantic ? OPT_pedantic : OPT_Wpointer_arith, 4193 "invalid application of %<sizeof%> to a function type"); 4194 else if (!complain) 4195 return error_mark_node; 4196 value = size_one_node; 4197 } 4198 else 4199 value = size_int (FUNCTION_BOUNDARY / BITS_PER_UNIT); 4200 } 4201 else if (type_code == VOID_TYPE || type_code == ERROR_MARK) 4202 { 4203 if (type_code == VOID_TYPE 4204 && complain && (pedantic || warn_pointer_arith)) 4205 pedwarn (loc, pedantic ? OPT_pedantic : OPT_Wpointer_arith, 4206 "invalid application of %qs to a void type", op_name); 4207 else if (!complain) 4208 return error_mark_node; 4209 value = size_one_node; 4210 } </code></pre>

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