gets() is dangerous because it is possible for the user to crash the program by typing too much into the prompt. It can't detect the end of available memory, so if you allocate an amount of memory too small for the purpose, it can cause a seg fault and crash. Sometimes it seems very unlikely that a user will type 1000 letters into a prompt meant for a person's name, but as programmers, we need to make our programs bulletproof. (it may also be a security risk if a user can crash a system program by sending too much data).

Fgets()允许您指定从标准输入缓冲区中取出多少字符，以便它们不会溢出变量。

gets() is dangerous because it is possible for the user to crash the program by typing too much into the prompt. It can't detect the end of available memory, so if you allocate an amount of memory too small for the purpose, it can cause a seg fault and crash. Sometimes it seems very unlikely that a user will type 1000 letters into a prompt meant for a person's name, but as programmers, we need to make our programs bulletproof. (it may also be a security risk if a user can crash a system program by sending too much data).

Fgets()允许您指定从标准输入缓冲区中取出多少字符，以便它们不会溢出变量。

因为gets在从stdin获取字节并将它们放到某个地方时不会做任何检查。举个简单的例子:

char array1[] = "12345";
char array2[] = "67890";

gets(array1);

首先，你可以输入你想要的字符数，get不会关心它。其次，字节超过数组的大小(在本例中为array1)将覆盖它们在内存中找到的任何内容，因为gets将写入它们。在前面的例子中，这意味着如果你输入"abcdefghijklmnopqrts"可能，不可预知的，它也会覆盖array2或其他东西。

该函数是不安全的，因为它假定输入一致。永远不要用它!

您不应该使用gets，因为它无法阻止缓冲区溢出。如果用户输入的数据超过了缓冲区的容量，您很可能会出现损坏或更糟的情况。

事实上，ISO实际上已经从C标准中删除了get(从C11开始，尽管它在C99中被弃用)，考虑到他们对向后兼容性的高度评价，这应该表明该函数有多糟糕。

正确的做法是将fgets函数与stdin文件句柄一起使用，因为您可以限制从用户读取的字符。

但这也有它的问题，如:

用户输入的额外字符将在下次读取。 没有用户输入过多数据的快速通知。

为此，几乎每一个C程序员在他们职业生涯的某个阶段都会编写一个更有用的fget包装器。这是我的:

#include <stdio.h>
#include <string.h>

#define OK       0
#define NO_INPUT 1
#define TOO_LONG 2
static int getLine (char *prmpt, char *buff, size_t sz) {
    int ch, extra;

    // Get line with buffer overrun protection.
    if (prmpt != NULL) {
        printf ("%s", prmpt);
        fflush (stdout);
    }
    if (fgets (buff, sz, stdin) == NULL)
        return NO_INPUT;

    // If it was too long, there'll be no newline. In that case, we flush
    // to end of line so that excess doesn't affect the next call.
    if (buff[strlen(buff)-1] != '\n') {
        extra = 0;
        while (((ch = getchar()) != '\n') && (ch != EOF))
            extra = 1;
        return (extra == 1) ? TOO_LONG : OK;
    }

    // Otherwise remove newline and give string back to caller.
    buff[strlen(buff)-1] = '\0';
    return OK;
}

用一些测试代码:

// Test program for getLine().

int main (void) {
    int rc;
    char buff[10];

    rc = getLine ("Enter string> ", buff, sizeof(buff));
    if (rc == NO_INPUT) {
        printf ("No input\n");
        return 1;
    }

    if (rc == TOO_LONG) {
        printf ("Input too long\n");
        return 1;
    }

    printf ("OK [%s]\n", buff);

    return 0;
}

它提供了与fgets相同的保护，它可以防止缓冲区溢出，但它也通知调用者发生了什么，并清除多余的字符，以便它们不会影响您的下一个输入操作。

随心所欲地使用它，我在此发布它的“做你该死的想做的事情”许可证:-)

额外的信息:

从man 3得到的Linux Ubuntu你会看到(强调):

描述 永远不要使用这个函数。

并且，从cppreference.com wiki这里(https://en.cppreference.com/w/c/io/gets)你会看到:Notes从不使用gets()。

笔记 gets()函数不执行边界检查，因此这个函数非常容易受到缓冲区溢出攻击。它不能安全使用(除非程序运行在限制stdin上可以显示内容的环境中)。因此，该函数在C99标准的第三个勘误表中已被弃用，并在C11标准中被完全删除。Fgets()和gets_s()是推荐的替换。 永远不要使用gets()。

如您所见，该函数在C11或更高版本中已完全弃用并被删除。

请使用fgets()或gets_s()。

下面是我使用fgets()的演示，带有完整的错误检查:

从read_stdin_fgets_basic_input_from_user.c:

#include <errno.h>   // `errno`
#include <stdio.h>   // `printf()`, `fgets()`
#include <stdlib.h>  // `exit()`
#include <string.h>  // `strerror()`

// int main(int argc, char *argv[])  // alternative prototype
int main()
{
    char buf[10];

    // NEVER USE `gets()`! USE `fgets()` BELOW INSTEAD!

    // USE THIS!: `fgets()`: "file get string", which reads until either EOF is
    // reached, OR a newline (`\n`) is found, keeping the newline char in
    // `buf`.
    // For `feof()` and `ferror()`, see:
    // 1. https://en.cppreference.com/w/c/io/feof
    // 1. https://en.cppreference.com/w/c/io/ferror
    printf("Enter up to %zu chars: ", sizeof(buf) - 1); // - 1 to save room
                                                        // for null terminator
    char* retval = fgets(buf, sizeof(buf), stdin);
    if (feof(stdin))
    {
        // Check for `EOF`, which means "End of File was reached".
        // - This doesn't really make sense on `stdin` I think, but it is a good
        //   check to have when reading from a regular file with `fgets
        //   ()`. Keep it here regardless, just in case.
        printf("EOF (End of File) reached.\n");
    }
    if (ferror(stdin))
    {
        printf("Error indicator set. IO error when reading from file "
               "`stdin`.\n");
    }
    if (retval == NULL)
    {
        printf("ERROR in %s(): fgets() failed; errno = %i: %s\n",
            __func__, errno, strerror(errno));

        exit(EXIT_FAILURE);
    }

    size_t num_chars_written = strlen(buf) + 1; // + 1 for null terminator
    if (num_chars_written >= sizeof(buf))
    {
        printf("Warning: user input may have been truncated! All %zu chars "
               "were written into buffer.\n", num_chars_written);
    }
    printf("You entered \"%s\".\n", buf);


    return 0;
}

示例运行和输出:

eRCaGuy_hello_world/c$ gcc -Wall -Wextra -Werror -O3 -std=c17 read_stdin_fgets_basic_input_from_user.c -o bin/a && bin/a
Enter up to 9 chars: hello world!
Warning: user input may have been truncated! All 10 chars were written into buffer.
You entered "hello wor".

eRCaGuy_hello_world/c$ gcc -Wall -Wextra -Werror -O3 -std=c17 read_stdin_fgets_basic_input_from_user.c -o bin/a && bin/a
Enter up to 9 chars: hey
You entered "hey
".

我最近在comp.lang.c的一篇USENET文章中读到，gets()将从标准中删除。哦吼

你会很高兴知道 委员会刚刚投票(一致通过) 将gets()从 还有草案。