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Laying Out Data Declarations
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For details on documenting data declarations, see Commenting Data Declarations in Section 32.5. For aspects of data use, see s 10 through 13.
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Use only one data declaration per line As shown in the examples above, you should give each data declaration its own line. It s easier to put a comment next to each declaration if each one is on its own line. It s easier to modify declarations because each declaration is selfcontained. It s easier to find specific variables because you can scan a single column rather than reading each line. It s easier to find and fix syntax errors because the line number the compiler gives you has only one declaration on it.
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Quickly in the data declaration in Listing 31-50, what type of variable is currentBottom
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Listing 31-50. C++ example of crowding more than one variable declaration onto a line.
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int rowIndex, columnIdx; Color previousColor, currentColor, nextColor; Point previousTop, previousBottom, currentTop, currentBottom, nextTop, nextBottom; Font previousTypeface, currentTypeface, nextTypeface; Color choices[ NUM_COLORS ];
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1 CODING HORROR
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This is an extreme example. But it is not too far removed from a much more common style shown in Listing 31-51:
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Listing 31-51. C++ example of crowding more than one variable declaration onto a line.
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int rowIndex, columnIdx; Color previousColor, currentColor, nextColor; Point previousTop, previousBottom, currentTop, currentBottom, nextTop, nextBottom; Font previousTypeface, currentTypeface, nextTypeface; Color choices[ NUM_COLORS ];
8 CODING HORROR
This is not an uncommon style of declaring variables, and the variable is still hard to find because all the declarations are jammed together. The variable s type is hard to find too. Now, what is nextColor s type in Listing 31-52
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31. Layout and Style
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Listing 31-52. C++ example of readability achieved by putting only one variable declaration on each line.
int rowIndex; int columnIdx; Color previousColor; Color currentColor; Color nextColor; Point previousTop; Point previousBottom; Point currentTop; Point currentBottom; Point nextTop; Point nextBottom; Font previousTypeface; Font currentTypeface; Font nextTypeface; Color choices[ NUM_COLORS ];
The variable nextColor was probably easier to find than nextTypeface was in Listing 31-51. This style is characterized by one declaration per line and a complete declaration including the variable type on each line. Admittedly, this style chews up a lot of screen space 20 lines instead of the 3 in the first example, although those 3 lines were pretty ugly. I can t point to any studies that show that this style leads to fewer bugs or greater comprehension. If Sally Programmer, Jr. asked me to review her code, however, and her data declarations looked like the first example, I d say, No way too hard to read. If they looked like the second example, I d say, Uh...maybe I ll get back to you. If they looked like the final example, I would say, Certainly it s a pleasure.
Declare variables close to where they re first used A style that s preferable to declaring all variables in a big block is to declare each variable close to where it s first used. This reduces span and live time and facilitates refactoring code into smaller routines when necessary. For more details, see Keep Variables Live for As Short a Time As Possible in Section 10.4. Order declarations sensibly In the example above, the declarations are grouped by types. Grouping by types is usually sensible since variables of the same type tend to be used in related operations. In other cases, you might choose to order them alphabetically by variable name. Although alphabetical ordering has many advocates, my feeling is that it s too much work for what it s worth. If your list of variables is so long that alphabetical ordering helps, your routine is probably too big. Break it up so that you have smaller routines with fewer variables.
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31. Layout and Style
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In C++, put the asterisk next to the variable name in pointer declarations or declare pointer types It s common to see pointer declarations that put the asterisk next to the type, as in Listing 31-53:
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