Sybase 12.4.2 manual Special considerations when passing character types, 272

Calling external libraries from procedures

Special considerations when passing character types

For the character data type (CHAR), Adaptive Server IQ allocates a 255-byte buffer (including one for the null terminator) for each parameter. If the parameter is an INOUT parameter, the existing value is copied into the buffer and null terminated, and a pointer to this buffer is passed to the external function. The external function should therefore not allocate a buffer of its own for OUT or INOUT character parameters: the server has already allocated the space. If the external function writes beyond the 256 bytes (including the ending null character), it is writing over data structures in the server.

When the entry point returns, the parameter buffers are translated back into their server data structure string equivalents based on the strlen() value of the buffer.

The external function should be sure to null-terminate any output string parameters. OUT parameters follow the same procedure except that as there is no initial data, no initial value of the output buffer parameter is guaranteed.

Always be sure to put a null byte into an OUT char parameter, as the lack of one could cause problems if the out buffer happens to be allocated adjacent to an area that is not in the allocate address space of the server.

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