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| <title>SWIG:Examples:tcl:constants</title> |
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| <tt>SWIG/Examples/tcl/constants/</tt> |
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| <H2>Wrapping C Constants</H2> |
| |
| <p> |
| When SWIG encounters C preprocessor macros and C declarations that look like constants, |
| it creates Tcl variables with an identical value. Click <a href="example.i">here</a> |
| to see a SWIG interface with some constant declarations in it. |
| |
| <h2>Accessing Constants from Tcl</h2> |
| |
| Click <a href="runme.tcl">here</a> to see a script that prints out the values |
| of the constants contained in the above file. |
| |
| <h2>Key points</h2> |
| |
| <ul> |
| <li>The values of preprocessor macros are converted into Tcl read-only variables. |
| <li>Types are inferred by syntax (e.g., "3" is an integer and "3.5" is a float). |
| <li>Character constants such as 'x' are converted into strings. |
| <li>C string literals such as "Hello World" are converted into strings. |
| <li>Macros that are not fully defined are simply ignored. For example: |
| <blockquote> |
| <pre> |
| #define EXTERN extern |
| </pre> |
| </blockquote> |
| is ignored because SWIG has no idea what type of variable this would be. |
| |
| <p> |
| <li>Expressions are allowed provided that all of their components are defined. Otherwise, the constant is ignored. |
| |
| <li>Certain C declarations involving 'const' are also turned into Tcl constants. |
| <li>The constants that appear in a SWIG interface file do not have to appear in any sort |
| of matching C source file since the creation of a constant does not require linkage |
| to a stored value (i.e., a value held in a C global variable or memory location). |
| <li>Since constants are turned into Tcl variables, you have to use the global |
| statement when accessing from a procedure. For example: |
| |
| <blockquote> |
| <pre> |
| proc foo {} { |
| global ICONST # Some C constant |
| puts $ICONST |
| } |
| </pre> |
| </blockquote> |
| </ul> |
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