C中不同的输出内容文件副本 [英] Different output content file copy in C

问题描述

你好，我在C语言中有一个简单的复制文件程序，但是当我使用第二种方法时，我无法解释为什么我在目标文件中得到了不同的输出. for循环的正确输出:

Hello i had a simple copy file program in C but i cant explain why i get different output in the destination file when i use the 2nd method. The correct output with for loop:

I am the worst programmer in the world!
:D
 And this is bla bla bla bla
 more bla bla bla...

使用while循环但在EOF中会生成随机字符的

BUT with while loop a random char is generated in EOF:

I am the worst programmer in the world!
:D
 And this is bla bla bla bla
 more bla bla bla...


代码是

int main()
{
int i;
char ch;
create_files();
FILE *src = fopen("best.txt", "r");
FILE *dst = fopen("copied.txt", "w");
for(i=getc(src); i!=EOF; i=getc(src))  //correct copy
    {
        putc(i, dst);
    }

/* while(!feof(src))                  //woot?
    {
        ch=fgetc(src);
        fputc(ch,dst);
    }*/

fclose(dst);
fclose(src);
return 0;
}

void create_files()
{
    FILE *fp;
    fp = fopen("best.txt","w");
    fprintf(fp,"I am the worst programmer in the world!\n:D\n And this is bla bla bla bla\n more bla bla bla...\n");
    fclose(fp);
}

我已经使用了fputc或putc以及fgetc或getc，并且仍然相同.我忘了什么吗?

i ve used both fputc or putc and fgetc or getc and still the same. Did i forget something?

推荐答案

什么

while (!feof(src)) {
    ch=fgetc(src);
    fputc(ch,dst);
}

确实是:

1. 检查EOF
2. 读取字符，可能导致EOF
3. 输出刚刚读取的字符，而不检查EOF.

当发生EOF时，在下一次迭代中的(1)检入之前，仍将执行(3).特殊值EOF转换为char并输出.

When EOF occurs, (3) is still executed before the check in (1) in the next iteration. The special value EOF is converted to a char and output.

正确的循环是

while ((ch = fgetc(src)) != EOF)
    fputc(ch, dst);

假设，您将ch的类型指定为int，因为char不能表示EOF.注意支票中的分配；一些程序员会告诉您这很丑陋，但是使用它的人太多了，您可能还不习惯.您的变体for循环也是正确的.

assuming you give ch the type int, because a char cannot represent EOF. Note the assignment within the check; some programmers will tell you that's ugly, but so many use it that you might as well get used to it. Your variant for loop is correct as well.

(除了1:fputc等同于putc，fgetc等同于getc，只要您不尝试在函数指针上下文中使用它们即可.)

(Aside 1: fputc is equivalent to putc and fgetc to getc, as long as you don't try to use them in a function pointer context.)

(除了2:您的while循环也不会检查流错误，而检查EOF也会返回捕获的错误.)

(Aside 2: your while loop also doesn't check for stream errors, while checking for EOF returns catches that as well.)

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