C- For 循环 gcc 中的 int 第一个声明

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为什么会这样C代码无法用 gcc 编译？

for(int j=0; j<n; j++){
 //some code here
}

我知道有一个解决方案，其中包括声明 j出For环形。但是，gcc中有任何选项吗？在C中做到这一点程序？

Answer 1

C99 及后者允许此功能。在 C99 模式 -std=C99 下编译代码。

C11:6.8.5.3 for 语句:

1 The statement

for ( clause-1 ; expression-2 ; expression-3 ) statement

behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration¹, the scope of any identifiers it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.158)

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_{1.重点是我的。}