掃描字符串時，如果用戶輸入超過30個字符，該如何禁止輸入？

Question

所以我有這樣的scanf

scanf ("%30[^\n]%c", &i 

我如何添加其中，如果用戶輸入超過30個字符，它會提示一個消息，說有太多的人物，並讓他們重新進入的條件？

這裏是我的整個循環不斷重新進入，直到輸入正確的，但我沒有合適的條件設定

int keeptrying = 1, rc; 
char after, i; 

do 
{ 
    rc = scanf ("%30[^\n]%c", &i, &after); 
     if (rc == 0) 
     { 
      printf (" **Invalid input try again: "); 
      clear(); 
     } 
      else if (after != '\n') 
      { 
       printf (" **Trailing characters try again: "); 
       clear(); 
      } 
       else if() // THIS IS WHERE I WOULD PUT THE CONDITION 
       { 
        printf (" **Title is longer than 30 characters: "); 
       } 
        else 
        { 
         keeptrying = 0; 
        } 

} while (keeptrying == 1); 

return i; 

Answer 1

基本上，你只是想在一條線上閱讀，並檢查如果其長度大於30要做到這一點，您可以使用strlen()，在線閱讀我建議使用類似getline代替：

int keeptrying = 1; 
char *line = NULL; 
size_t linecap = 0; 

do { 
    ssize_t rc = getline(&line, &linecap, stdin); 
    if (rc == 0) 
    { 
     printf ("End of file."); 
     exit(1); 
    } 
    else if (strlen(line) > 30) 
    { 
     printf (" **Title is longer than 30 characters: "); 
    } 
    else 
    { 
     keeptrying = 0; 
    } 
} while (keeptrying == 1); 

// Use line 

free(line); 

Answer 2

可以scanf函數後使用的getchar（也明確標準輸入） ：

do 
{ 
    char i[31]; 
    rc = scanf ("%30[^\n]", &i); 
     if (rc == 0) 
     { 
      printf (" **Invalid input try again: "); 
      clear(); 
     } 
      else if (getchar() != '\n') 
      { 
       printf (" more than 30 characters try again: "); 
       clear(); 
      } 
        else 
        { 
         keeptrying = 0; 
        } 

} while (keeptrying == 1);