Imagecraft c compiler and development environment for the atmel avr

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ICCV8 for AVR – C Compiler for Atmel AVRthey are not the same thing. For example, an array has storage space associated withit, whereas you must initialize a pointer to point to some valid space before accessingit.Structure / Union TypeFor whatever reasons, some beginners seem to have a lot of trouble with the structdeclaration. The basic form isstruct [tag] { member-declaration * } [variable list];The following are valid examples of declaring a struct variable:1) struct { int junk; } var1;2) struct tag1 { int junk; } var2;3) struct tag2;struct tag2 { int junk; };struct tag2 var3;The tag is optional and is useful if you want to refer to the same struct type again(for example, you can use struct tag1 to declare more variables of that type). In C,within the same file, even if you have two identical-looking struct declarations, theyare different struct types. In the examples above, all of the structs have differenttypes, even though their struct types look identical.However, in the case of separate files, this rule is relaxed: if two structs have thesame declaration, then they are equivalent. This makes sense, since in C, it isimpossible to have a single declaration to appear in more than one file. Declaring thestruct in a header file still means that a separate (but identical-looking) declarationappears in each file that #include the header file.Function PrototypeIn the old days of C, it was sometimes acceptable to call a function without declaring itfirst -- everything would work correctly anyway. However, with the ImageCraftcompilers, it is important to declare a function before referencing it, including the typesof the function arguments. Otherwise, it is possible that the compiler will not generatethe correct code. When you declare a function with a complete argument and returntype information, it’s called the function prototype of the function.76
ICCV8 for AVR – C Compiler for Atmel AVRExpressions and Type PromotionsSemicolon TerminationThe expression statement is one of the few statements in C that requires asemicolon termination. The others are break, continue, return, goto, and dostatements. Sometimes you see things like:#define foo blah blah;...void bar() { ... };Those semicolons at the end are most likely extraneous and can possibly even causeyour program to fail subtly (to compile or to execute).lvalue and rvalueEvery expression produces a value. If the expression is on the left-hand side of anassignment, it is called an lvalue. In all other cases, an expression produces a rvalue.An lvalue is either the name of a variable, an array element reference, a pointerdereference, or a struct/union field member; everything else is not a valid lvalue. Acommon question is why does the compiler complain about((char *)pc)++and the answer is that type cast does not produce an lvalue. Some compilers mayaccept it as an extension, but it is not part of the standard C. This is an example of thecorrect method of incrementing a cast variable:unsigned pc;...pc = (unsigned)((char *)pc + 1);Integer ConstantsInteger constants are either decimal (default), octal (starting with 0), or hexadecimal(0x or 0X). Our compilers support the extension of using 0b as a prefix for binaryconstants. You can explicitly change the type of an integer constant by adding U/u, L/l, or combinations of them. The type of an integer is the first type of each list in thefollowing table that can hold the value of the constant:77
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