當嘗試為多個平臺編譯以下(簡化)代碼時,我發現它在某些方面是失敗的,即IBM的xlC_r.進一步的調查發現,它也沒有進來和cl..它與g和Solaris的CC成功編譯.

這是代碼：

int main()

{

int a1[1];

bool a2[1];

for (int *it = a1, *end = a1+1; it != end; ++it) {

//...

bool *jt = a2, *end = a2+1;

//...

}

}

xlC_r錯誤：

"main.cpp", line 8.25: 1540-0400 (S) "end" has a conflicting declaration.

"main.cpp", line 6.25: 1540-0425 (I) "end" is defined on line 6 of "main.cpp".

ang子錯誤：

main.cpp:8:25: error: redefinition of 'end' with a different type

bool *jt = a2, *end = a2+1;

^

main.cpp:6:25: note: previous definition is here

for (int *it = a1, *end = a1+1; it != end; ++it) {

^

來錯誤：

"ComeauTest.c", line 8: error: "end", declared in for-loop initialization, may not

be redeclared in this scope

bool *jt = a2, *end = a2+1;

^

問題是為什么這是一個錯誤？

看看2003年的標準,它說如下(6.5.3)：

The for statement

for ( for-init-statement; condition; expression ) statement

is equivalent to

{

for-init-statement;

while ( condition ) {

statement;

expression;

}

}

except that names declared in the for-init-statement are in the same

declarative-region as those declared in condition

這里沒有聲明的名稱.

另外,它說(6.5.1)：

When the condition of a while statement is a declaration, the scope

of the variable that is declared extends from its point of declaration

(3.3.1) to the end of the while statement. A while statement of the form

while (T t = x) statement

is equivalent to

label:

{

T t = x;

if (t) {

statement;

goto label;

}

}

再次,我不知道這是相關的,因為沒有聲明在條件.所以給出6.5.3的等效重寫,我的代碼應該是一樣的：

int main()

{

int a1[1];

bool a2[1];

{

int *it = a1, *end = a1+1;

while (it != end) {

//...

bool *jt = a2, *end = a2+1;

//...

++it;

}

}

}

這顯然會允許結束重新聲明.

總結

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