请问程序的执行总是从主要用C开始？ [英] Does the program execution always start from main in C?

问题描述

必须编程从主执行开始，或者可以在起始地址被修改？

 的#include＆LT;＆stdio.h中GT;无效的乐趣（）;启动的#pragma乐趣诠释的main（）
{
    的printf（主）;
    返回0;
}无效的乐趣（）
{
    的printf（在乐趣）;
}
 

此程序打印在乐趣在主。

解决方案

  

在'的#pragma'命令在ANS​​I标准中规定有一个任意实现定义的效果。在GNU C preprocessor的#pragma'首先尝试运行游戏'流氓';如果失败，它会尝试运行游戏'黑客';如果失败，它会尝试运行GNU Emacs的显示汉诺塔方案;如果失败，它报告一个致命错误。在任何情况下，preprocessing不会继续。

- 理查德M. Stallman的，在GNU C preprocessor，版本1.34

开始执行程序在启动code或运行。这通常是 _start 或者叫一些汇编程序例程诸如此类，位于（在Unix机器上）在文件的crt0.o 的自带的编译器包。它运行一个C的可执行文件（如所需的设置，设立标准输入，标准输出和标准错误，由的atexit（） ...为C ++还包括初始化全局对象，即运行其构造函数）。只有这样做控制跳转到的main（）。

由于我的答案当然presses开始的报价雄辩地，是什么的#pragma 不完全取决于你的编译器。检查其文档。 （我猜你的编译启动 - 这应该是的方式以＃ ppended $ P $ - 通知运行时调用乐趣（）第一...）

Must program execution start from main, or can the starting address be modified?

#include <stdio.h>

void fun();

#pragma startup fun

int main()
{
    printf("in main");
    return 0;
}

void fun()
{
    printf("in fun");
}

This program prints in fun before in main.

解决方案

The '#pragma' command is specified in the ANSI standard to have an arbitrary implementation-defined effect. In the GNU C preprocessor, '#pragma' first attempts to run the game 'rogue'; if that fails, it tries to run the game 'hack'; if that fails, it tries to run GNU Emacs displaying the Tower of Hanoi; if that fails, it reports a fatal error. In any case, preprocessing does not continue.

-- Richard M. Stallman, The GNU C Preprocessor, version 1.34

Program execution starts at the startup code, or "runtime". This is usually some assembler routine called _start or somesuch, located (on Unix machines) in a file crt0.o that comes with the compiler package. It does the setup required to run a C executable (like, setting up stdin, stdout and stderr, the vectors used by atexit()... for C++ it also includes initializing of global objects, i.e. running their constructors). Only then does control jump to main().

As the quote at the beginning of my answer expresses so eloquently, what #pragma does is completely up to your compiler. Check its documentation. (I'd guess your pragma startup - which should be prepended with a # by the way - tells the runtime to call fun() first...)

这篇关于请问程序的执行总是从主要用C开始？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！