如果我不包含头文件会发生什么 [英] What will happen if I don't include header files

问题描述

如果我在运行 c 程序时不包含头文件会怎样?我知道我会收到警告，但程序运行良好.

What will happen if I don't include the header files when running a c program? I know that I get warnings, but the programs runs perfectly.

我知道头文件包含函数声明.因此，当我不包含它们时，编译器是如何计算出来的?它会检查所有头文件吗?

I know that the header files contain function declarations. Therefore when I don't include them, how does the compiler figure it out? Does it check all the header files?

推荐答案

我知道我收到了警告，但程序运行良好.

I know that I get warnings, but the programs runs perfectly.

这是 ANSI C 之前的不幸遗留问题:该语言不需要函数原型，因此标准 C 直到今天仍然允许它(通常会产生警告以查找没有原型调用的函数).

That is an unfortunate legacy of pre-ANSI C: the language did not require function prototypes, so the standard C allows it to this day (usually, a warning can be produced to find functions called without a prototype).

当你调用一个没有原型的函数时，C 编译器会对被调用的函数做出假设:

When you call a function with no prototype, C compiler makes assumptions about the function being called:

• 函数的返回类型假定为 int
• 假定所有参数都已声明(即没有 ... 可变参数)
• 假定所有参数都是您在默认促销之后传递的任何参数，依此类推.

如果在没有原型的情况下调用的函数符合这些假设，那么您的程序将正确运行；否则，这是未定义的行为.

If the function being called with no prototype fits these assumptions, your program will run correctly; otherwise, it's undefined behavior.

这篇关于如果我不包含头文件会发生什么的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！