C++文件格式和輸出到文件

Question

假設我有一段代碼，打印的東西，這樣，

u_int packetCount = 0; 
    while (int returnValue = pcap_next_ex(pcap, &header, &data) >= 0) 
    { 

     // Show the packet number 
     printf("Packet # %i\n", ++packetCount); 

     // Show the size in bytes of the packet 
     printf("Packet size: %d bytes\n", header->len); 

     // Show a warning if the length captured is different 
     if (header->len != header->caplen) 
      printf("Warning! Capture size different than packet size: %ld bytes\n", header->len); 

     // Show Epoch Time 
     printf("Epoch Time: %d:%d seconds\n", header->ts.tv_sec, header->ts.tv_usec); 

     // loop through the packet and print it as hexidecimal representations of octets 
     // We also have a function that does this similarly below: PrintData() 
     for (u_int i=0; (i < header->caplen) ; i++) 
     { 
      // Start printing on the next after every 16 octets 
      if ((i % 16) == 0) printf("\n"); 

      // Print each octet as hex (x), make sure there is always two characters (.2). 
      printf("%.2x ", data[i]); 

     } 

     // Add two lines between packets 
     printf("\n\n"); 
    } 

最後一行讓我像

Packet # 39 
Packet size: 54 bytes 
Epoch Time: 1084443432:328438 seconds 

fe ff 20 00 01 00 00 00 01 00 00 00 08 00 45 00 
00 28 0f 5c 40 00 80 06 91 d8 91 fe a0 ed 41 d0 
e4 df 0d 2c 00 50 38 af ff f3 11 4c a9 48 50 10 
24 14 31 71 00 00 

Packet # 40 
Packet size: 54 bytes 
Epoch Time: 1084443445:216971 seconds 

00 00 01 00 00 00 fe ff 20 00 01 00 08 00 45 00 
00 28 c0 ad 40 00 2f 06 31 87 41 d0 e4 df 91 fe 
a0 ed 00 50 0d 2c 11 4c a9 48 38 af ff f3 50 11 
19 20 3c 64 00 00 

Packet # 41 
Packet size: 54 bytes 
Epoch Time: 1084443445:216971 seconds 

fe ff 20 00 01 00 00 00 01 00 00 00 08 00 45 00 
00 28 0f 5f 40 00 80 06 91 d5 91 fe a0 ed 41 d0 
e4 df 0d 2c 00 50 38 af ff f3 11 4c a9 49 50 10 
24 14 31 70 00 00 

Packet # 42 
Packet size: 54 bytes 
Epoch Time: 1084443457:374452 seconds 

fe ff 20 00 01 00 00 00 01 00 00 00 08 00 45 00 
00 28 0f 62 40 00 80 06 91 d2 91 fe a0 ed 41 d0 
e4 df 0d 2c 00 50 38 af ff f3 11 4c a9 49 50 11 
24 14 31 6f 00 00 

我需要打印輸出該行的輸出「printf("%.2x ", data[i]); 」，然後將此輸出寫入C++中的文件。我可以請知道如何做到這一點？

Answer 1

查看fstream標準庫。寫入文件的示例可在here找到。

Answer 2

使用std::setw和std::hex來控制寬度以及如何打印數字。 std::dec會帶你回到十進制（基10）格式。用std::setfill('0')填零。

[我要指出的是，在所有已知的實現，fstream將調用printf [或更可能snprintf或一些類似的功能]內，所以它不是多大的收穫，不是「它看起來像C++」等使用fstream在fprintf ]