短文件上的 C fread() 在文件结束后会产生垃圾

Question

我的教授指定将 file_1.txt 一次读取 100 字节到 char 数组 中。我生成了以下代码片段:

int key;
key = atoi(argv[1]);
FILE *file_pointer;
file_pointer = fopen(argv[2], "rb");
char buffer[100];
char output[sizeof(int)][100];
int output_counter = 0;
int read_counter;
int read_elements;

while(read_elements = fread(buffer, 1, 100, file_pointer) > 0)
{  
    read_counter = 0;    
    while(read_counter < 100)
    {

        printf("xor'ing %d and %d\n", key, buffer[read_counter]);
        output[output_counter][read_counter] = buffer[read_counter] ^ key;
        read_counter = read_counter + 1;
    }

    output_counter = output_counter + 1;
}

fclose(file_pointer);

file_1.txt 内容为:“项目的测试文件\n”。我使用了gccencrypt.c然后:

./a.out 111 file_1.txt file_2.txt

然后: ./a.out 111 file_2.txt file_3.txt

cat file_3.txt reads: 

项目的测试文件:

v▒▒▒s▒▒@/////////▒

第一次运行带有 file_1.txt 和 file_2.txt 的程序时，嵌套 while 循环中的 print 语句打印:

xor'ing 111 and 116

xor'ing 111 and 101

xor'ing 111 and 115

xor'ing 111 and 116

xor'ing 111 and 32

xor'ing 111 and 102

xor'ing 111 and 105

xor'ing 111 and 108

xor'ing 111 and 101

xor'ing 111 and 32

xor'ing 111 and 102

xor'ing 111 and 111

xor'ing 111 and 114

xor'ing 111 and 32

xor'ing 111 and 116

xor'ing 111 and 104

xor'ing 111 and 101

xor'ing 111 and 32

xor'ing 111 and 112

xor'ing 111 and 114

xor'ing 111 and 111

xor'ing 111 and 106

xor'ing 111 and 101

xor'ing 111 and 99

xor'ing 111 and 116

xor'ing 111 and 10

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 118

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and -88

xor'ing 111 and -31

xor'ing 111 and -94

xor'ing 111 and 2

xor'ing 111 and -120

xor'ing 111 and 127

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and -57

xor'ing 111 and 115

xor'ing 111 and -33

xor'ing 111 and 2

xor'ing 111 and -120

xor'ing 111 and 127

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 1

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and -19

xor'ing 111 and 9

xor'ing 111 and 64

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 47

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and 0

xor'ing 111 and -96

xor'ing 111 and 9

xor'ing 111 and 64

xor'ing 111 and 0

这些随机元素来自哪里？

Answer 1

在使用 fread() 之前将缓冲区字符数组的所有元素初始化为 0，从而消除了垃圾。