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Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 44 |
1 files changed, 44 insertions, 0 deletions
@@ -54686,6 +54686,50 @@ parameter, since unsafe callbacks do not use it. .cble +.coNP Macro @ deffi-var +.synb +.mets (deffi-var < name < var-expr << type ) +.syne +.desc +The +.code deffi-var +macro defines a global symbol macro which expands to an expression +accessing a foreign variable, creating the illusion that the +variable is available as a Lisp variable holding a Lisp data type. + +The +.meta name +argument gives the name of the macro. + +The +.meta var-expr +argument must evaluate to a +.code cptr +object which holds a pointer to the address of the foreign +variable. + +The +.meta type +argument expresses the variable type in FFI type syntax. + +Once the variable is defined, accessing the macro symbol +.meta name +performs a get operation on the foreign variable, yielding +the conversion of that variable to a Lisp value. +An assignment to the symbol performs a put operation, +converting a Lisp object to a value which overwrites +the object. + +Note: FFI memory management is not helpful in the use of +variables. Suppose a string value is +stored in a variable of type +.codn str . +This means that FFI dynamically allocates a buffer which +stores the UTF-8 encoded version of the string, and this +buffer is placed into the foreign variable. +Then suppose another such assignment takes place. +The previous value is simply overwritten without being +freed. .coNP Macro @ typedef .synb .mets (typedef < name << type-syntax ) |