C: 如何使用 getc 来避免产生非 UTF-8 字符？

Question

我目前正在编写一个 c 程序，它将采用 3 个参数、两个文件(一个输入和一个输出)和一个 int(输出行的最大长度，称之为 x)。我想读取输入文件中的每一行并将前 x 个字符写入输出文件(有效地“修剪”文件)。

这是我的代码:

int main(int argc, char *argv[]) {

  const char endOfLine = '\n';

  if (argc < 4) {
    printf("Program takes 4 params\n");
    exit(1);
  } else {
    // Convert character argument [3] (line length) to an int
    int maxLen = atoi(argv[3]);

    char str[maxLen];
    char *inputName;
    char *outputName;

    inputName = argv[1];
    outputName = argv[2];

    // Open files to be read and written to
    FILE *inFile = fopen(inputName, "r");
    FILE *outFile = fopen(outputName, "w");

    int count = 0;
    char ch = getc(inFile);
    while (ch != EOF) {
        if (ch == '\n') {
          str[count] = (char)ch;
          printf("Adding %s to output\n", str);
          fputs(str, outFile);
          count = 0;
        } else if (count < maxLen) {
          str[count] = ch;
          printf("Adding %c to str\n", ch);
          count++;
        } else if (count == maxLen) {
          str[count] = '\n';
        }
        ch = getc(inFile);
    }

  }

  return 0;
}

唯一的问题是，如果最后一个字符是单引号，它会打印出非 UTF-8 字符，如下所示:

For Whom t
John Donne
No man is 
Entire of 
Each is a 
A part of 
If a clod 
Europe is 
As well as
As well as
Or of thin
Each man��
For I am i
Therefore,
For whom t

Answer 1

您可以检查最后一个字符输出是否为 utf-8 连续字节 10xxxxxx，如果是，则继续输出直到字符完成。

// bits match 10xxxxxx
int is_utf_continue_byte(int ch){
    return ch & 0x80 && ~ch & 0x40;
}

//...
while (is_utf_continue_byte(ch))
    putchar(ch), ch = getchar();