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| 41 | <a name="id2861760"></a> |
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| 42 | How to control the library order on Unix? |
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| 43 | </h2></div></div></div> |
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| 44 | <p>On the Unix-like operating systems, the order in which static |
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| 45 | libraries are specified when invoking the linker is important, because by |
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| 46 | default, the linker uses one pass though the libraries list. Passing the |
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| 47 | libraries in the incorrect order will lead to a link error. Further, this |
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| 48 | behaviour is often used to make one library override symbols from |
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| 49 | another. So, sometimes it's necessary to force specific order of |
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| 50 | libraries. |
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| 51 | </p> |
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| 52 | <p>Boost.Build tries to automatically compute the right order. The |
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| 53 | primary rule is that if library a "uses" library b, then library a will |
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| 54 | appear on the command line before library b. Library a is considered to |
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| 55 | use b is b is present either in the sources of a or in its |
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| 56 | requirements. To explicitly specify the use relationship one can use the |
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| 57 | <use> feature. For example, both of the following lines will cause |
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| 58 | a to appear before b on the command line: |
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| 59 | </p> |
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| 60 | <pre class="programlisting"> |
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| 61 | lib a : a.cpp b ; |
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| 62 | lib a : a.cpp : <use>b ; |
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| 63 | </pre> |
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| 64 | <p> |
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| 65 | The same approach works for searched libraries, too: |
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| 66 | </p> |
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| 67 | <pre class="programlisting"> |
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| 68 | lib z ; |
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| 69 | lib png : : <use>z ; |
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| 70 | exe viewer : viewer png z ; |
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