执行程序时，可以从命令行传值给 C 程序。这些值被称为命令行参数，它们对程序很重要，特别是当您想从外部控制程序，而不是在代码内对这些值进行硬编码时，就显得尤为重要了。
在 C 语言中，命令行参数是一种从命令行获取输入的方法，可以用于运行程序时传递信息给程序。命令行参数通过 main 函数的参数传递给程序。main 函数的原型可以是如下两种形式之一：
int main(int argc, char *argv[]);
或者:
int main(int argc, char **argv);
-
argc (argument count): 表示命令行参数的数量，包括程序名本身。因此，argc 至少为 1。
-
argv (argument vector): 是一个指向字符串数组的指针，其中每个字符串是一个命令行参数。数组的第一个元素（即 argv[0]）通常是程序的名称。接下来的元素是传递给程序的命令行参数。
下面是一个简单的实例，检查命令行是否有提供参数，并根据参数执行相应的动作：
实例
#include <stdio.h>
int main( int argc, char *argv[] )
{
if( argc == 2 )
{
printf("The argument supplied is %s\\n", argv[1]);
}
else if( argc > 2 )
{
printf("Too many arguments supplied.\\n");
}
else
{
printf("One argument expected.\\n");
}
}
使用一个参数，编译并执行上面的代码，它会产生下列结果：
$./a.out testing
The argument supplied is testing
使用两个参数，编译并执行上面的代码，它会产生下列结果：
$./a.out testing1 testing2
Too many arguments supplied.
不传任何参数，编译并执行上面的代码，它会产生下列结果：
$./a.out
One argument expected
应当指出的是，argv[0] 存储程序的名称，argv[1] 是一个指向第一个命令行参数的指针，*argv[n] 是最后一个参数。如果没有提供任何参数，argc 将为 1，否则，如果传递了一个参数，argc 将被设置为 2。
多个命令行参数之间用空格分隔，但是如果参数本身带有空格，那么传递参数的时候应把参数放置在双引号 "" 或单引号 '' 内部。让我们重新编写上面的实例，有一个空格，那么你可以通过这样的观点，把它们放在双引号或单引号""""。让我们重新编写上面的实例，向程序传递一个放置在双引号内部的命令行参数：
实例
#include <stdio.h>
int main( int argc, char *argv[] )
{
printf("Program name %s\\n", argv[0]);
if( argc == 2 )
{
printf("The argument supplied is %s\\n", argv[1]);
}
else if( argc > 2 )
{
printf("Too many arguments supplied.\\n");
}
else
{
printf("One argument expected.\\n");
}
}
使用一个用空格分隔的简单参数，参数括在双引号中，编译并执行上面的代码，它会产生下列结果：
$./a.out "testing1 testing2"
Progranm name ./a.out
The argument supplied is testing1 testing2
使用场景
命令行参数在许多情况下都很有用，例如：
- 配置文件路径
- 模式选择（例如调试模式）
- 输入文件和输出文件名
- 运行时选项和标志（如 -v 表示详细模式）
注意事项
- 命令行参数通常是字符串，如果需要将其转换为数值类型，可以使用标准库函数如 atoi 或 strtol。
- 应该始终验证和处理命令行参数，以防止输入错误或恶意输入。
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