MT4・MT5 コンパイルエラー・警告 エラー（コンパイルできない）
expression of 'void' type is illegal
- エラー番号
error 151- 意味
- 戻り値のない（void）関数の結果を使おうとした
「expression of 'void' type is illegal」とは
void 型の関数（戻り値がない関数）の結果を、変数に代入したり計算に使ったりしたときのコンパイルエラーです。
MetaEditor での表示例
| MT4 | error 151: 'f' - expression of 'void' type is illegal |
|---|---|
| MT5 | error 151: expression of 'void' type is illegal |
実際のログでは先頭に「ファイル名(行,列) :」が付きます。ログの行をダブルクリックすると、エラーの場所にカーソルが移動します。表示は 2026年9月の MetaEditor で確認したもので、ビルドによって細部が変わることがあります。
「expression of 'void' type is illegal」の主な原因
- void 関数の戻り値を int a = f(); のように受け取った
「expression of 'void' type is illegal」の対処法
- 値を返したいなら関数の型を int や double に変え、return で値を返す
- 値が不要なら f(); だけで呼ぶ
関連するエラー
コンパイルエラー・警告の解説一覧
- undeclared identifier
- semicolon expected
- unexpected token
- unexpected token, probably type is missing?
- some operator expected
- unexpected end of program
- unbalanced parentheses
- closing quote '"' expected
- wrong parameters count
- function already defined and has body
- variable already defined
- function must have a body
- function not defined
- not all control paths return a value
- function must return a value
- expression of 'void' type is illegal
- event handling function not found
- function declared with wrong type or/and parameters
- possible loss of data due to type conversion
- truncation of constant value
- implicit conversion from 'number' to 'string'
- return value of 'OrderSend' should be checked
- declaration hides global variable
- l-value required
- constant cannot be modified
- constant expression required
- invalid index value
- array required
- arrays are passed by reference only
- parameter conversion not allowed
- illegal operation use
- illegal 'else' without matching 'if'
- 'break' must be used within some loop or switch statement
- case value already used
- ambiguous call to overloaded function
- can't open include file
- unknown property
- identifier already used
- struct member undefined
- struct or class type expected
- private member access error
- cannot instantiate abstract class
- structures or classes containing objects are not allowed
- function declarations are allowed on global, namespace or class scope only
- name expected
- division by zero in the constant expression
- expression has no effect
- expression not boolean
- sign mismatch
- possible use of uninitialized variable
- empty controlled statement found
- macro redefinition
- call resolves to … due to new rules of method hiding
- cannot be used for static allocated array
