c - 字符串突然变空，即使它在片刻之前是完整的

Question

我正在尝试为命令行输入编写一个简单的 C 函数来检查用户的输入是否太长。我留下了调试打印以显示发生了什么。

bool read_line(char str[])
{
    char c = '\0';
    int max_chars = sizeof(str) / sizeof(char);
    printf("%d\n", max_chars);
    int i = 0;
    while (true) {
        c = getchar();
        if (c == '\n' || c == EOF) {
            break;
        }
        printf("The value of c is %c\n", c);
        i++;
        printf("The value of i is %d\n", i);
        if (i > max_chars) {
            return false;
        }
        printf("Inserting character %c\n", c);
        str[i] = c;
        printf("str[i] is %c\n", str[i]);
    }

    return true;
}

测试代码为:

char str[] = {[0 ... SIZE - 1] = 0};
bool length_valid = read_line(str);
if (!length_valid) {
    printf("Input too long\n");
    return 1;
}
puts(str);
return 0;

这是运行程序的输出；我输入了“forth”这一行。

8
forth
The value of c is f
The value of i is 1
Inserting character f
str[i] is f
The value of c is o
The value of i is 2
Inserting character o
str[i] is o
The value of c is r
The value of i is 3
Inserting character r
str[i] is r
The value of c is t
The value of i is 4
Inserting character t
str[i] is t
The value of c is h
The value of i is 5
Inserting character h
str[i] is h
8
forth
The value of c is f
The value of i is 1
Inserting character f
str[i] is f
The value of c is o
The value of i is 2
Inserting character o
str[i] is o
The value of c is r
The value of i is 3
Inserting character r
str[i] is r
The value of c is t
The value of i is 4
Inserting character t
str[i] is t
The value of c is h
The value of i is 5
Inserting character h
str[i] is h
<Empty line>

该字符串在片刻之前清楚地显示为充满了字符，但不知何故在其间它变成了空值。

Answer 1

EOF 有点正确，但更简单的解决方法是使 max_chars 成为如下参数:

bool read_line(char str[], int max_chars)

...然后调用它:

bool length_valid = read_line(str, sizeof(str));

...这应该可以帮助您完成大部分工作。