C解析器异常重复输出

Question

[好吧，请忍受我，因为这里有些奇怪的东西。我目前正在尝试使用最多20个char命令且没有管道等实现一个SUPER简单外壳。我也在一起学习C，因此，请原谅任何严重的错误或用法。

这是我的解析器代码：

#include <dirent.h>
#include <stdlib.h>
#include <stdio.h>

int main(void) {
    int running = 1;

    /* Main loop */
    while(running==1) {
        // The max size of the input is 20 bytes
        char input[20];
        // Read string from user
        fgets(input, sizeof(input), stdin);

        /* ----- PARSE INPUT ----- */
        char buffer[20];
        for(int i = 0; i < sizeof(input); i++) {
            buffer[i] = input[i];
            /* ------ CHECK BUFFER AGAINST VARIOUS COMMANDS ----- */
            // TALK TO THE HAND
            if (strcmp(buffer, "TALK TO THE HAND") == 0) {
                // execute TALK TO THE HAND
                printf("TALK TO THE HAND\n");
            }
            else {
                printf("WHAT DID I DO WRONG?\n");
            }
        }
    }
}

输入TALK TO THE HAND时的预期输出就是它的回音，但我得到的是：

TALK TO THE HAND
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
TALK TO THE HAND
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?
WHAT DID I DO WRONG?

而且我不知道为什么它似乎在不同的输出中反复循环。

Answer 1

代码迭代太远

迭代到字符串的长度，而不是缓冲区的大小。

    // for(int i = 0; i < sizeof(input); i++) {
    for(int i = 0; input[i]; i++) {

无论如何，都不需要此迭代。只需比较input

//if (strcmp(buffer, "TALK TO THE HAND") == 0) {
if (strcmp(input, "TALK TO THE HAND") == 0) {

不考虑已读取的'\n'。

圈闭电位'\n'

fgets(input, sizeof(input), stdin);
// add
input[strcspn(input, "\n")] = '\0';

缓冲区太小

[buffer[]需要容纳20个字符，'\n'和'\0'。

// char input[20];
char input[20 + 1 + 1];

---

高级

[fgets()可能返回NULL，这表明stdin已关闭。

用户输入的文本可能太多，很容易检测到

#define INPUT_N 20
//                extra  \n  \0
char input[INPUT_N + 1 + 1 + 1]; // I'd just go with INPUT_N*2

if (fgets(input, sizeof(input), stdin) == NULL) {
  fprintf(stderr, "Input closed\n");
  return EXIT_FAILURE;
}

size_t len = strlen(input);
if (len > 0 && input[len-1] == '\n') {
  input[--len] = '\0';  // lop off \n
}

if (len > INPUT_N) {
  // exit or otherwise cope with too much data
  fprintf(stderr, "Excessive long input\n");
  return EXIT_FAILURE;
}

...