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12.2.2 Enabling and Disabling Warnings

The warning function also allows you to control which warnings are actually printed to the screen. If the warning function is called with a string argument that is either "on" or "off" all warnings will be enabled or disabled.

It is also possible to enable and disable individual warnings through their string identifications. The following code will issue a warning

warning ("non-negative-variable", 
         "'a' must be non-negative. Setting 'a' to zero.");

while the following won't issue a warning

warning ("off", "non-negative-variable");
warning ("non-negative-variable", 
         "'a' must be non-negative. Setting 'a' to zero.");

The functions distributed with Octave can issue one of the following warnings.

Octave:array-to-scalar

If the Octave:array-to-scalar warning is enabled, Octave will warn when an implicit conversion from an array to a scalar value is attempted. By default, the Octave:array-to-scalar warning is disabled.

Octave:array-to-vector

If the Octave:array-to-vector warning is enabled, Octave will warn when an implicit conversion from an array to a vector value is attempted. By default, the Octave:array-to-vector warning is disabled.

Octave:assign-as-truth-value

If the Octave:assign-as-truth-value warning is enabled, a warning is issued for statements like

if (s = t)
  ...

since such statements are not common, and it is likely that the intent was to write

if (s == t)
  ...

instead. There are times when it is useful to write code that contains assignments within the condition of a while or if statement. For example, statements like

while (c = getc())
  ...

are common in C programming. It is possible to avoid all warnings about such statements by disabling the Octave:assign-as-truth-value warning, but that may also let real errors like

if (x = 1)  # intended to test (x == 1)!
  ...

slip by. In such cases, it is possible suppress errors for specific statements by writing them with an extra set of parentheses. For example, writing the previous example as

while ((c = getc()))
  ...

will prevent the warning from being printed for this statement, while allowing Octave to warn about other assignments used in conditional contexts. By default, the Octave:assign-as-truth-value warning is enabled.

Octave:associativity-change

If the Octave:associativity-change warning is enabled, Octave will warn about possible changes in the meaning of some code due to changes in associativity for some operators. Associativity changes have typically been made for Matlab compatibility. By default, the Octave:associativity-change warning is enabled.

Octave:divide-by-zero

If the Octave:divide-by-zero warning is enabled, a warning is issued when Octave encounters a division by zero. By default, the Octave:divide-by-zero warning is enabled.

Octave:empty-list-elements

If the Octave:empty-list-elements warning is enabled, a warning is issued when an empty matrix is found in a matrix list. For example,

a = [1, [], 3, [], 5]

By default, the Octave:empty-list-elements warning is enabled.

Octave:fortran-indexing

If the Octave:fortran-indexing warning is enabled, a warning is printed for expressions which select elements of a two-dimensional matrix using a single index. By default, the Octave:fortran-indexing warning is disabled.

Octave:function-name-clash

If the Octave:function-name-clash warning is enabled, a warning is issued when Octave finds that the name of a function defined in a function file differs from the name of the file. (If the names disagree, the name declared inside the file is ignored.) By default, the Octave:function-name-clash warning is enabled.

Octave:future-time-stamp

If the Octave:future-time-stamp warning is enabled, Octave will print a warning if it finds a function file with a time stamp that is in the future. By default, the Octave:future-time-stamp warning is enabled.

Octave:imag-to-real

If the Octave:imag-to-real warning is enabled, a warning is printed for implicit conversions of complex numbers to real numbers. By default, the Octave:imag-to-real warning is disabled.

Octave:matlab-incompatible

Print warnings for Octave language features that may cause compatibility problems with Matlab.

Octave:missing-semicolon

If the Octave:missing-semicolon warning is enabled, Octave will warn when statements in function definitions don't end in semicolons. By default the Octave:missing-semicolon warning is disabled.

Octave:neg-dim-as-zero

If the Octave:neg-dim-as-zero warning is enabled, print a warning for expressions like

eye (-1)

By default, the Octave:neg-dim-as-zero warning is disabled.

Octave:num-to-str

If the Octave:num-to-str warning is enable, a warning is printed for implicit conversions of numbers to their ASCII character equivalents when strings are constructed using a mixture of strings and numbers in matrix notation. For example,

[ "f", 111, 111 ]
=> "foo"

elicits a warning if the Octave:num-to-str warning is enabled. By default, the Octave:num-to-str warning is enabled.

Octave:precedence-change

If the Octave:precedence-change warning is enabled, Octave will warn about possible changes in the meaning of some code due to changes in precedence for some operators. Precedence changes have typically been made for Matlab compatibility. By default, the Octave:precedence-change warning is enabled.

Octave:reload-forces-clear

If several functions have been loaded from the same file, Octave must clear all the functions before any one of them can be reloaded. If the Octave:reload-forces-clear warning is enabled, Octave will warn you when this happens, and print a list of the additional functions that it is forced to clear. By default, the Octave:reload-forces-clear warning is enabled.

Octave:resize-on-range-error

If the Octave:resize-on-range-error warning is enabled, print a warning when a matrix is resized by an indexed assignment with indices outside the current bounds. By default, the Octave:resize-on-range-error warning is disabled.

Octave:separator-insert

Print warning if commas or semicolons might be inserted automatically in literal matrices.

Octave:single-quote-string

Print warning if a single quote character is used to introduce a string constant.

Octave:str-to-num

If the Octave:str-to-num warning is enabled, a warning is printed for implicit conversions of strings to their numeric ASCII equivalents. For example,

"abc" + 0
=> 97 98 99

elicits a warning if the Octave:str-to-num warning is enabled. By default, the Octave:str-to-num warning is disabled.

Octave:string-concat

If the Octave:string-concat warning is enabled, print a warning when concatenating a mixture of double and single quoted strings. By default, the Octave:string-concat warning is disabled.

Octave:undefined-return-values

If the Octave:undefined-return-values warning is disabled, print a warning if a function does not define all the values in the return list which are expected. By default, the Octave:undefined-return-values warning is enabled.

Octave:variable-switch-label

If the Octave:variable-switch-label warning is enabled, Octave will print a warning if a switch label is not a constant or constant expression. By default, the Octave:variable-switch-label warning is disabled.