1 false and 0 true

Question

I came across an is equals   function in a c API at work that returned 1 for non-equal sql tables  false  and 0 for equal ones  true   I only realized it after running test cases on my code  one for the positive example and one for the negative and they both failed which at first made little sense  The code in the API does not have a bug as the output was recorded correctly in its documentation   My questions - are there upside down worlds   parallel universes   coding languages where this logical NOTing is normal  Isn t 1 usually true  Is the coder of the API making an error

User · Answer

I suspect it s just following the Linux   Unix standard for returning 0 on success   Does it really say  1  is false and  0  is true

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It is common for comparison functions to return 0 on  equals   so that they can also return a negative number for  less than  and a positive number for  greater than    strcmp   and memcmp   work like this   It is  however  idiomatic for zero to be false and nonzero to be true  because this is how the C flow control and logical boolean operators work   So it might be that the return values chosen for this function are fine  but it is the function s name that is in error  it should really just be called compare   or similar

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This upside-down-world is common with process error returns  The shell variable    reports the return value of the previous program to execute from the shell  so it is easy to tell if a program succeeds or fails     false   echo    1   true   echo    0   This was chosen because there is a single case where a program succeeds but there could be dozens of reasons why a program fails -- by allowing there to be many different failure error codes  a program can determine why another program failed without having to parse output   A concrete example is the aa-status program supplied with the AppArmor mandatory access control tool      Upon exiting  aa-status will set its return value to the    following values      0   if apparmor is enabled and policy is loaded      1   if apparmor is not enabled loaded      2   if apparmor is enabled but no policy is loaded      3   if the apparmor control files aren t available under         sys kernel security       4   if the user running the script doesn t have enough        privileges to read the apparmor control files     I m sure there are more widely-spread programs with this behavior  but I know this one well

User · Answer

There s no good reason for 1 to be true and 0 to be false  that s just the way things have always been notated  So from a logical perspective  the function in your API isn t  wrong   per se   That said  it s normally not advisable to work against the idioms of whatever language or framework you re using without a damn good reason to do so  so whoever wrote this function was probably pretty bone-headed  assuming it s not simply a bug

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I m not sure if I m answering the question right  but here s a familiar example   The return type of GetLastError   in Windows is nonzero if there was an error  or zero otherwise  The reverse is usually true of the return value of the function you called

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It may very well be a mistake on the original author  however the notion that 1 is true and 0 is false is not a universal concept   In shell scripting 0 is returned for success  and any other number for failure   In other languages such as Ruby  only nil and false are considered false  and any other value is considered true  so in Ruby both 1 and 0 would be considered true

[c] 1 = false and 0 = true?

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