示例：读取文件

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
//exit()
#include <stdlib.h>

int main(int argc, char* argv[])
{
	int ch; //读取文件时，储存每个字符的地方
	FILE* fp; //文件指针
	unsigned long count = 0;
	if (argc != 2)
	{
		printf("Usage: %s filename\n", argv[0]);
		exit(EXIT_FAILURE);
	}
	//printf("file path: %s", argv[1]);
	if ((fp = fopen(argv[1], "r")) == NULL)
	{
		printf("Can't open %s\n", argv[1]);
		exit(EXIT_FAILURE);
	}
	while ((ch = getc(fp)) != EOF)
	{
		putc(ch, stdout); //与putchar(ch);相同
		count++;
	}
	//如果成功关闭,fclose()函数返回0，否则返回EOF
	//如果磁盘已满，移动硬盘被移除或出现I/O错误，都会导致调用fclose()函数失败
	if (fclose(fp) != 0) //关闭fp指定的文件，必要时刷新缓冲区
		printf("Error in closing file %s\n", argv[1]);
	printf("\nFile %s has %lu characters\n", argv[1], count);

	system("pause");
	return 0;
}

运行测试