c - 动态大小字符数组中的运行时错误

Question

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

int main(void) {
  int i = 0;
  char c, *input;
  input = (char *) malloc(sizeof(char));

  if(input == NULL) {
    printf("NOT ENOUGH SPACE!");
    exit(1);
  }

  printf("Input a string, press ENTER when done: ");

  while((c = getchar()) != '\n') {
    realloc(input, (sizeof(char)));
    input[i++] = c;
  }

  input[i] = '\0';
  printf("\nYou've entered the string: %s\n", input);
}

上面的代码片段适用于小输入。但是只要提供的输入很大，它就会失败。存在运行时错误或段错误。内存空间的重新分配可能有一些错误。我基本上想从用户动态存储一个字符数组，即不提及用户可以直接放入任何大小的字符数组的输入容量。

Answer 1

这里的逻辑是错误的:

  while((c = getchar()) != '\n') {
      realloc(input, (sizeof(char)));
      input[i++] = c;
  }

您实际上并没有增加缓冲区的大小，而且您还丢弃了 realloc 的结果。

尝试:

  while ((c = getchar()) != '\n') {
    // Note: you need one extra character for the terminator, so for the
    // first char, when `i` is 0, then you need room for two `char`s in
    // the buffer - one for the first input character and one for the
    // terminator. And so on...
    char * temp = realloc(input, i + 2); // NB: realloc can, and sometimes does, fail
    if (temp == NULL) // if realloc failed then exit program
        exit(1);
    input = temp;     // otherwise update input...
    input[i++] = c;
  }

---

此外，由于您总是要对每个字符调用 realloc(顺便说一下，这是非常低效的，但它有效)，这一行:

input = (char *) malloc(sizeof(char));

(不应该有类型转换，顺便说一句，因为这是 C，而不是 C++)可以是:

input = NULL;

---

最后一个错误:

char c;

应该是:

int c;

否则您的 while 循环可能永远不会终止，因为 EOF 只能正确表示为 int。

---

所以最终的固定程序应该是这样的:

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

int main(void) {
    int i = 0;
    int c;
    char * input = NULL;

    printf("Input a string, press ENTER when done: ");

    while ((c = getchar()) != '\n') {
        // Note: you need one extra character for the terminator, so for the
        // first char, when `i` is 0, then you need room for two `char`s in
        // the buffer - one for the first input character and one for the
        // terminator. And so on...
        char * temp = realloc(input, i + 2); // NB: realloc can, and sometimes does, fail
        if (temp == NULL) // if realloc failed then exit program
            exit(1);
        input = temp;     // otherwise update input...
        input[i++] = c;
    }

    input[i] = '\0';
    printf("\nYou've entered the string: %s\n", input);

    return 0;
}