//命令行
# include <stdio.h>
# include <stdlib.h>
# define BUFSIZE 2048

void write_in(FILE* source, FILE* dest);

int main(int argc, char* argv[])
{
    FILE* fa;  //一个指向目标文件，一个指向源文件
    FILE* fs;
    int ch;


    if (argc != 3)
    {
        printf("Your argument is wrong.\n");
        exit(EXIT_FAILURE);
    }
    if ((fs = fopen(argv[1], "rb")) == NULL)                  //以二进制模式打开文件
    {
        fprintf(stdout, "Can't open the source file %s.\n", argv[1]);
        exit(0);
    }
    if ((fa = fopen(argv[2], "w+b")) == NULL)
    {
        fprintf(stdout, "Can't open the aim file %s.\n", argv[2]);
        exit(0);
    }
    
    
    while ((ch = getc(fs)) != EOF)
        putc(ch,fa);
        
    puts("DONE.");
    fclose(fa);     //可以添加检测是否关闭了文件的语句
    fclose(fs);

    return 0;
}

//交互的方式
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <ctype.h>

# define SLEN 20
char* s_gets(char *st, int n);

int main()
{
    FILE* fa;  //一个指向目标文件，一个指向源文件
    FILE* fs;
    int ch;

    char source[SLEN];  
    char target[SLEN];
    
    puts("Enter the name of the source file.");
    s_gets(source, SLEN);
    if ((fs = fopen(source, "r")) == NULL)                      //以文本模式
    {
        fprintf(stdout, "Can't open the source file %s.\n", source);
        exit(0);
    }
    puts("Enter the name of the target file.");
    s_gets(target, SLEN);
    if (strcmp(source, target) == 0)
    {
        printf("Can't copy the file to himself.");
        exit(EXIT_FAILURE);
    }
    if ((fa = fopen(target, "w+")) == NULL)
    {
        fprintf(stdout, "Can't open the target file %s.\n", target);
        exit(0);
    }
    
    while ((ch = getc(fs)) != EOF)
    {
        
        putc(toupper(ch), fa);    //将文本转为大写
    }
    fclose(fs);
    rewind(fa);

    while ((ch = getc(fa)) != EOF)
        putchar(ch);

    puts("DONE.");
    fclose(fa);

    return 0;
}

char * s_gets(char *st, int n)
{
    char* ret_val;
    char* find;

    ret_val = fgets(st, n, stdin);
    if (ret_val)
    {
        find = strrchr(st, '\n');
        if (find)
            *find = '\0';
        else
            while (getchar() != '\n')
                continue;
    }
    return ret_val;
}