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Scalar(3pm) User Contributed Perl Documentation Scalar(3pm)


Convert::Scalar - convert between different representations of perl scalars


 use Convert::Scalar;


This module exports various internal perl methods that change the internal representation or state of a perl scalar. All of these work in-place, that is, they modify their scalar argument. No functions are exported by default.

The following export tags exist:

 :utf8   all functions with utf8 in their name
 :taint  all functions with taint in their name
 :refcnt all functions with refcnt in their name
 :ok     all *ok-functions.
Returns true when the given scalar is marked as utf8, false otherwise. If the optional mode argument is given, also forces the interpretation of the string to utf8 (mode true) or plain bytes (mode false). The actual (byte-) content is not changed. The return value always reflects the state before any modification is done.

This function is useful when you "import" utf8-data into perl, or when some external function (e.g. storing/retrieving from a database) removes the utf8-flag.

Similar to "utf8 scalar, 1", but additionally returns the scalar (the argument is still modified in-place).
Similar to "utf8 scalar, 0", but additionally returns the scalar (the argument is still modified in-place).
Returns true if the bytes inside the scalar form a valid utf8 string, false otherwise (the check is independent of the actual encoding perl thinks the string is in).
Convert the string content of the scalar in-place to its UTF8-encoded form (and also returns it).
Attempt to convert the string content of the scalar from UTF8-encoded to ISO-8859-1. This may not be possible if the string contains characters that cannot be represented in a single byte; if this is the case, it leaves the scalar unchanged and either returns false or, if "fail_ok" is not true (the default), croaks.
Convert the string value of the scalar to UTF8-encoded, but then turn off the "SvUTF8" flag so that it looks like bytes to perl again. (Might be removed in future versions).
Returns the number of characters in the string, counting wide UTF8 characters as a single character, independent of whether the scalar is marked as containing bytes or mulitbyte characters.
$old = readonly scalar[, $new]
Returns whether the scalar is currently readonly, and sets or clears the readonly status if a new status is given.
Sets the readonly flag on the scalar.
Clears the readonly flag on the scalar.
Remove the specified magic from the scalar (DANGEROUS!).
Weaken a reference. (See also WeakRef).
Taint the scalar.
returns true when the scalar is tainted, false otherwise.
Remove the tainted flag from the specified scalar.
Returns SvLEN (scalar), that is, the actual number of bytes allocated to the string value, or "undef", is the scalar has no string value.
Sets the memory area used for the scalar to the given length, if the current length is less than the new value. This does not affect the contents of the scalar, but is only useful to "pre-allocate" memory space if you know the scalar will grow. The return value is the modified scalar (the scalar is modified in-place).
Reserves enough space in the scalar so that addlen bytes can be appended without reallocating it. The actual contents of the scalar will not be affected. The modified scalar will also be returned.

This function is meant to make append workloads efficient - if you append a short string to a scalar many times (millions of times), then perl will have to reallocate and copy the scalar basically every time.

If you instead use "extend $scalar, length $shortstring", then Convert::Scalar will use a "size to next power of two, roughly" algorithm, so as the scalar grows, perl will have to resize and copy it less and less often.

Calls "extend scalar, addlen" to ensure some space is available, then do the equivalent of "sysread" to the end, to try to fill the extra space. Returns how many bytes have been read, 0 on EOF or undef> on error, just like "sysread".

This function is useful to implement many protocols where you read some data, see if it is enough to decode, and if not, read some more, where the naive or easy way of doing this would result in bad performance.

Tries to read "length" bytes into "scalar". Unlike "read" or "sysread", it will try to read more bytes if not all bytes could be read in one go (this is often called "xread" in C).

Returns the total nunmber of bytes read (normally "length", unless an error or EOF occurred), 0 on EOF and "undef" on errors.

Like "readall", but for writes - the equivalent of the "xwrite" function often seen in C.
Returns the current reference count of the given scalar and optionally sets it to the given reference count.
Increments the reference count of the given scalar inplace.
Decrements the reference count of the given scalar inplace. Use "weaken" instead if you understand what this function is fore. Better yet: don't use this module in this case.
Works like "refcnt", but dereferences the given reference first. This is useful to find the reference count of arrays or hashes, which cannot be passed directly. Remember that taking a reference of some object increases it's reference count, so the reference count used by the *_rv-functions tend to be one higher.
Works like "refcnt_inc", but dereferences the given reference first.
Works like "refcnt_dec", but dereferences the given reference first.
Calls SvOK, SvUOK, SvROK, SvPOK, SvNOK or SvNIOK on the given scalar, respectively.


The following API functions (perlapi) are considered for future inclusion in this module If you want them, write me.

 the sv2xx family


 Marc Lehmann <>
2020-11-09 perl v5.32.0