I'm looking at this page which says:
我在看这页上面写着:
In C++ you can declare variables pretty much anywhere in your program. This is not the case with C. Variables must be declared at the beginning of a function and must be declared before any other code. This includes loop counter variables, which means you can't do this:
在c++中，几乎可以在程序的任何地方声明变量。C.变量必须在函数的开头声明，并且必须在任何其他代码之前声明。这包括循环计数器变量，这意味着您不能这样做:
for(int i = 0; i < 200; i++) {
for(int i = 0;我< 200;我+ +){
Forgetting that you can't declare variables just anywhere is one of the most frequent causes of 'it won't compile' problems for programmers moving from C++ to C.
对于从c++迁移到C的程序员来说，忘记不能在任何地方声明变量是导致“它不会编译”问题的最常见原因之一。
I've been using Objective-C for a while, and thus C, and I have no problems with a statement such as for(int i = 0; i < 200; i++) { and yet Objective-C is C, strictly, so what is this web page referring to?
我使用Objective-C已经有一段时间了，因此C，对于for(int I = 0;我< 200;但是Objective-C严格来说是C，那么这个网页指的是什么呢?
1 个解决方案
#1
6
The web page is inaccurately characterizing C89.
web页面对C89的描述不准确。
In C89, you could declare variables at the top of any block (not just at the start of a function), but not at any point during a block.
在C89中，您可以在任何块的顶部声明变量(不只是在函数的开头)，但不能在块的任何位置声明变量。
In C99 and beyond, you are not constrained to declare variables at the beginning of a block. Specifically, C99 allows you to write:
在C99和beyond中，您不必在块的开头声明变量。具体来说，C99允许你写:
for (int i = 0; i < max; i++)
If you use GCC but need to retain compatibility with MSVC, then you can use -Wdeclaration-after-statement to detect when you declare a variable after a statement (which C89 does not allow).
如果您使用GCC但需要保持与MSVC的兼容性，那么您可以使用- wdeclaration - afterstatement来检测在语句之后(C89不允许)声明变量的时间。
Objective C presumably uses C99 rather than C89 as the standard it extends, so it allows variable declarations when needed.
Objective C使用C99而不是C89作为标准扩展，因此在需要时允许变量声明。
#1
6
The web page is inaccurately characterizing C89.
web页面对C89的描述不准确。
In C89, you could declare variables at the top of any block (not just at the start of a function), but not at any point during a block.
在C89中，您可以在任何块的顶部声明变量(不只是在函数的开头)，但不能在块的任何位置声明变量。
In C99 and beyond, you are not constrained to declare variables at the beginning of a block. Specifically, C99 allows you to write:
在C99和beyond中，您不必在块的开头声明变量。具体来说，C99允许你写:
for (int i = 0; i < max; i++)
If you use GCC but need to retain compatibility with MSVC, then you can use -Wdeclaration-after-statement to detect when you declare a variable after a statement (which C89 does not allow).
如果您使用GCC但需要保持与MSVC的兼容性，那么您可以使用- wdeclaration - afterstatement来检测在语句之后(C89不允许)声明变量的时间。
Objective C presumably uses C99 rather than C89 as the standard it extends, so it allows variable declarations when needed.
Objective C使用C99而不是C89作为标准扩展，因此在需要时允许变量声明。