c('PL_compare')

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- Reference manual
  - Foreign Language Interface
    - The Foreign Include File
      - Miscellaneous
        
        Term Comparison
        
        PL_compare()
        
        PL_same_compound()
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Availability:C-language interface function

int PL_compare(term_t t1, term_t t2)

Compares two terms using the standard order of terms and returns -1, 0 or 1. See also compare/3. If the terms are cyclic terms that have no order (see section 4.6.1) and the Prolog flag incomparable is error, it raises an exception and returns -2. -2 is also returned if the comparison raises a resource error. Code that tests the result using < 0 must first test for -2.