需要在我的printf轉換規範上設置字段寬度的指針

Question

這是一個基本的東西，但我需要指示如何設置字段寬度，以便表格可以很好地整齊地打印所有允許的值。我一直在玩它一段時間，並有麻煩。是否有一些技巧可以快速找出它？只是在正確的方向推動將不勝感激。

//Print the results in a table 
printf("\n#============================================#\n"); 
printf("| Description     | Input Data |\n"); 
printf("|============================================|\n"); 
printf("| Loan amount     | $ %8.2f |\n", loan); 
printf("| Yearly interest rate  |  %6.2f% |\n", rate); 
printf("| Number of years    |  %d  |\n", years); 
printf("|============================================|\n"); 
printf("| Payment Details    | Results |\n"); 
printf("|============================================|\n"); 
printf("| The monthly payment will be | $  %5.2f |\n", monthlyPayment); 
printf("| Interest paid    | $ %6.2f |\n", interestEarned); 
printf("#============================================#\n\n"); 

Answer 1

格式化數據比科學更接近藝術。

1. 考慮到項目壽命期間的字段寬度將會改變（更可能增長）。

2. 便於維護的郵政編碼。第一次絕對不對。性能不是那麼關鍵，因爲輸出無論如何都是CPU週期的一個漏洞。

3. 重複使用格式。

4. 字符串字面量避免fprintf()，改用fputs()。

5. RTFM fprintf()並讓最小寬度指定符爲您的朋友。

6. 小心一個格式的孤獨"%"。應該"%%"

第一次嘗試：

double loan, rate, monthlyPayment, interestEarned; 
    loan = interestEarned = monthlyPayment = 12345.78; 
    rate = 999.99; 
    int years = 30; 

    // Let us assume interesting part of the table is 10 wide 

    // 10 = 
    // .max_width 
    const char *fdash = "%s%.10s%s"; 

    // space, 8 char, space 
    // - left justify 
    // min_width.max_width 
    const char *ftext = "%s %-8.8s %s"; 

    // $, 8 width with 2 dec. places, space 
    // width.precision 
    const char *fcash = "%s$%8.2f %s"; 

    // space, 7 width, %, space 
    // width.precision 
    const char *fperc = "%s %7.2f%% %s"; 

    // space, 8 wide, space 
    // width 
    const char *fyear = "%s %8d %s"; 
    const char *bar = "=================================="; // extra long 

    fputs("\n", stdout); 
    printf(fdash, "#==============================", bar   , "#\n"); 
    printf(ftext, "| Description     |", "Input Data" , "|\n"); 
    printf(fdash, "|==============================", bar   , "|\n"); 
    printf(fcash, "| Loan amount     |", loan   , "|\n"); 
    printf(fperc, "| Yearly interest rate  |", rate   , "|\n"); 
    printf(fyear, "| Number of years    |", years   , "|\n"); 
    printf(fdash, "|==============================", bar   , "|\n"); 
    printf(ftext, "| Payment Details    |", "Results"  , "|\n"); 
    printf(fdash, "|==============================", bar   , "|\n"); 
    printf(fcash, "| The monthly payment will be |", monthlyPayment, "|\n"); 
    printf(fcash, "| Interest paid    |", interestEarned, "|\n"); 
    printf(fdash, "#==============================", bar   , "#\n"); 
    fputs("\n", stdout); 

輸出：字段太小"Input Data"。修復留給用戶。

#========================================# 
| Description     | Input Da | 
|========================================| 
| Loan amount     |$12345.78 | 
| Yearly interest rate  | 999.99% | 
| Number of years    |  30 | 
|========================================| 
| Payment Details    | Results | 
|========================================| 
| The monthly payment will be |$12345.78 | 
| Interest paid    |$12345.78 | 
#========================================#