c - getline中第二个参数的作用是什么？

Question

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

int main(void)
{
    char* buffer = malloc(100 * sizeof(char));
    size_t n = 3;

    getline(&buffer, &n, stdin);
    printf("%s\n", buffer);
    free(buffer);
}

我认为 getline 中的第二个参数 size_t *n 是限制读取的字符数。但是当我尝试使用更大的输入时，它仍然读取所有输入。我在手册页和网上进行了搜索，但找不到答案。谁能帮我解释一下吗？

Answer 1

来自getline man pages :

给定ssize_t getline(char **lineptr, size_t *n, FILE *stream);

If *lineptr is NULL, then getline() will allocate a buffer for storing the line, which should be freed by the user program. (In this case, the value in *n is ignored.)

Alternatively, before calling getline(), *lineptr can contain a pointer to a malloc(3)-allocated buffer *n bytes in size. If the buffer is not large enough to hold the line, getline() resizes it with realloc(3), updating *lineptr and *n as necessary.

强调我的。简而言之，更新 n 以确保线条适合。