c-从文件中读取行

Question

我是 c 语言新手，但我想从文件中读取文本。我不知道文件第一行的长度，那么如何为fgets函数编写正确的参数呢？现在我有:

char read[30]; // but I really don't know how long the line will be

while(fgets(read, sizeof(read), fp).......

Answer 1

您必须不断重新分配并附加到缓冲区，直到到达行尾。代码并不漂亮，但没有使用标准 C 库的简单替代方案:

char read[30];
char *line;
int len, total;

line = NULL;
total = 0;

do {
  if (fgets(read, sizeof(read), fp) == NULL)
    break;

  len = strlen(read);

  if (total == 0) {
    total = len;
    line = (char *)malloc(len);
    strcpy(line, read);
  } else {
    total += len;
    line = (char *)realloc(line, total);
    strcat(line, read);
  }
} while (read[len - 1] != '\n');