Has TRUE always had a non-zero value?

Question

I have a co-worker that maintains that TRUE used to be defined as 0 and all other values were FALSE. I could swear that every language I\'ve worked with, if you could even

Answer 1

Several functions in the C standard library return an 'error code' integer as result. Since noErr is defined as 0, a quick check can be 'if it's 0, it's Ok'. The same convention carried to a Unix process' 'result code'; that is, an integer that gave some inidication about how a given process finished.

In Unix shell scripting, the result code of a command just executed is available, and tipically used to signify if the command 'succeeded' or not, with 0 meaning success, and anything else a specific non-success condition.

From that, all test-like constructs in shell scripts use 'success' (that is, a result code of 0) to mean TRUE, and anything else to mean FALSE.

On a totally different plane, digital circuits frecuently use 'negative logic'. that is, even if 0 volts is called 'binary 0' and some positive value (commonly +5v or +3.3v, but nowadays it's not rare to use +1.8v) is called 'binary 1', some events are 'asserted' by a given pin going to 0. I think there's some noise-resistant advantages, but i'm not sure about the reasons.

Note, however that there's nothing 'ancient' or some 'switching time' about this. Everything I know about this is based on old conventions, but are totally current and relevant today.

Answer 2

For the most part, false is defined as 0, and true is non-zero. Some programming languages use 1, some use -1, and some use any non-zero value.

For Unix shells though, they use the opposite convention.

Most commands that run in a Unix shell are actually small programs. They pass back an exit code so that you can determine whether the command was successful (a value of 0), or whether it failed for some reason (1 or more, depending on the type of failure).

This is used in the sh/ksh/bash shell interpreters within the if/while/until commands to check conditions:

if command
then
   # successful
fi

If the command is successful (ie, returns a zero exit code), the code within the statement is executed. Usually, the command that is used is the [ command, which is an alias for the test command.

Answer 3

I can't recall TRUE being 0. 0 is something a C programmer would return to indicate success, though. This can be confused with TRUE.

It's not always 1 either. It can be -1 or just non-zero.

Answer 4

The SQL Server Database Engine optimizes storage of bit columns. If there are 8 or less bit columns in a table, the columns are stored as 1 byte. If there are from 9 up to 16 bit columns, the columns are stored as 2 bytes, and so on. The string values TRUE and FALSE can be converted to bit values: TRUE is converted to 1 and FALSE is converted to 0. Converting to bit promotes any nonzero value to 1.

Every language can have 0 as true or false So stop using number use words true Lol Or t and f 1 byte storage

Answer 5

I worked at a company with a large amount of old C code. Some of the shared headers defined their own values for TRUE and FALSE, and some did indeed have TRUE as 0 and FALSE as 1. This led to "truth wars":

/* like my constants better */
#undef TRUE
#define TRUE 1

#undef FALSE
#define FALSE 0

Answer 6

In the C language, before C++, there was no such thing as a boolean. Conditionals were done by testing ints. Zero meant false and any non-zero meant true. So you could write

if (2) {
  alwaysDoThis();
} else {
  neverDothis();
}

Fortunately C++ allowed a dedicated boolean type.