为什么 C 中的 argv(参数向量)定义为指针，并且需要将其第零个定义为程序名称? [英] Why is argv (argument vector) in C defined as a pointer and what is the need for defining its zeroth as the program name?

问题描述

#include <stdio.h>
int main(int argc, char *argv[])
{
 int i;
 for(i=1;i<argc;i++)
  printf("%s%s", argv[i], (i<argc-1)? " ":"");
 printf("\n");
 return 0;
} 

上面给出的是一个简单的 C 程序，它输出命令行输入.这里 argc 是参数计数器.argv 被认为是一个包含参数的数组.我的问题是:为什么它定义为指向字符数组而不是普通数组的指针?还有什么需要将其第零个元素(argv[0])定义为调用程序的名称.

Given above is a simple C program that outputs command line inputs. Here argc is the argument counter. argv is said to be an array that contains arguments. My question is: why does it define as a pointer to a character array instead of a normal array? Also what is the need for defining its zeroth element (argv[0]) as the name by which the program is invoked.

我是初学者，请从高层次的角度解释一下.

I am a beginner and please explain it high level perspective.

推荐答案

argv 被定义为指针而不是数组，因为 C 中没有数组参数这样的东西.

argv is defined as a pointer rather than as an array because there is no such thing as an array parameter in C.

argv>

您可以定义一些看起来像数组参数的东西，但它在编译时调整"为数组类型；例如，这两个声明完全等效:

You can define something that looks like an array parameter, but it's "adjusted" to array type at compile time; for example, these two declarations are exactly equivalent:

int foo(int param[]);
int foo(int param[42]); /* the 42 is quietly ignored */
int foo(int *param);    /* this is what the above two declarations really mean */

而main的定义可以写成:

int main(int argc, char *argv[]) { /* ... */ }

或作为

int main(int argc, char **argv) { /* ... */ }

两者完全相同(第二个，恕我直言，更清楚地表达了实际情况).

The two are exactly equivalent (and the second one, IMHO, more clearly expresses what's actually going on).

从某种意义上说，数组类型是 C 中的二等类型.操作数组的代码几乎总是通过指向元素的指针进行操作，执行指针算术以遍历元素.

Array types are, in a sense, second-class types in C. Code that manipulates array almost always does so via pointers to the elements, performing pointer arithmetic to traverse the elements.

comp.lang.c FAQ 的第 6 节解释了数组和指针之间经常令人困惑的关系.

Section 6 of the comp.lang.c FAQ explains the often confusing relationship between arrays and pointers.

(如果你被告知数组是真正的"指针，那么它们不是；数组和指针是不同的东西.)

(And if you've been told that arrays are "really" pointers, they're not; arrays and pointers are distinct things.)

至于为什么argv[0]指向程序名，那只是因为它有用.一些程序在错误消息中打印他们的名字；其他人可能会根据调用它们的名称来改变它们的行为.将程序名称与命令行参数捆绑在一起是一个相当随意的选择，但它很方便且有效.

As for why argv[0] points to the program name, that's just because it's useful. Some programs print their names in error messages; others may change their behavior depending on the name by which they're invoked. Bundling the program name with the command-line arguments was a fairly arbitrary choice, but it's convenient and it works.

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