如何创建文件 .csv？

Question

如何创建文件 .csv？，我只想创建一个文件，因为我想在 main() 之外声明我的文件。我也有一个函数和 de main() 函数。

我是这样的：https://www.tcpdump.org/sniffex.c 我想在我的文件 .csv 中写一些打印，例如 ip、tcp 等。

#define APP_NAME        "sniffex"
#define APP_DESC        "Sniffer example using libpcap"
#define APP_COPYRIGHT   "Copyright (c) 2005 The Tcpdump Group"
#define APP_DISCLAIMER  "THERE IS ABSOLUTELY NO WARRANTY FOR THIS PROGRAM."

#include <pcap.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

/* default snap length (maximum bytes per packet to capture) */
#define SNAP_LEN 1518

/* ethernet headers are always exactly 14 bytes [1] */
#define SIZE_ETHERNET 14

/* Ethernet addresses are 6 bytes */
#define ETHER_ADDR_LEN  6
FILE *f = fopen("test", "w");

/* Ethernet header */
struct sniff_ethernet {
        u_char  ether_dhost[ETHER_ADDR_LEN];    /* destination host address */
        u_char  ether_shost[ETHER_ADDR_LEN];    /* source host address */
        u_short ether_type;                     /* IP? ARP? RARP? etc */
};

/* IP header */
struct sniff_ip {
        u_char  ip_vhl;                 /* version << 4 | header length >> 2 */
        u_char  ip_tos;                 /* type of service */
        u_short ip_len;                 /* total length */
        u_short ip_id;                  /* identification */
        u_short ip_off;                 /* fragment offset field */
        #define IP_RF 0x8000            /* reserved fragment flag */
        #define IP_DF 0x4000            /* dont fragment flag */
        #define IP_MF 0x2000            /* more fragments flag */
        #define IP_OFFMASK 0x1fff       /* mask for fragmenting bits */
        u_char  ip_ttl;                 /* time to live */
        u_char  ip_p;                   /* protocol */
        u_short ip_sum;                 /* checksum */
        struct  in_addr ip_src,ip_dst;  /* source and dest address */
};
#define IP_HL(ip)               (((ip)->ip_vhl) & 0x0f)
#define IP_V(ip)                (((ip)->ip_vhl) >> 4)

/* TCP header */
typedef u_int tcp_seq;

struct sniff_tcp {
        u_short th_sport;               /* source port */
        u_short th_dport;               /* destination port */
        tcp_seq th_seq;                 /* sequence number */
        tcp_seq th_ack;                 /* acknowledgement number */
        u_char  th_offx2;               /* data offset, rsvd */
#define TH_OFF(th)      (((th)->th_offx2 & 0xf0) >> 4)
        u_char  th_flags;
        #define TH_FIN  0x01
        #define TH_SYN  0x02
        #define TH_RST  0x04
        #define TH_PUSH 0x08
        #define TH_ACK  0x10
        #define TH_URG  0x20
        #define TH_ECE  0x40
        #define TH_CWR  0x80
        #define TH_FLAGS        (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR)
        u_short th_win;                 /* window */
        u_short th_sum;                 /* checksum */
        u_short th_urp;                 /* urgent pointer */
};

void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);

void
print_payload(const u_char *payload, int len);

void
print_hex_ascii_line(const u_char *payload, int len, int offset);

void
print_app_banner(void);

void
print_app_usage(void);

/*
 * app name/banner
 */
void
print_app_banner(void)
{

    printf("%s - %s\n", APP_NAME, APP_DESC);
    printf("%s\n", APP_COPYRIGHT);
    printf("%s\n", APP_DISCLAIMER);
    printf("\n");

return;
}

/*
 * print help text
 */
void
print_app_usage(void)
{

    printf("Usage: %s [interface]\n", APP_NAME);
    printf("\n");
    printf("Options:\n");
    printf("    interface    Listen on <interface> for packets.\n");
    printf("\n");

return;
}

/*
 * print data in rows of 16 bytes: offset   hex   ascii
 *
 * 00000   47 45 54 20 2f 20 48 54  54 50 2f 31 2e 31 0d 0a   GET / HTTP/1.1..
 */
void
print_hex_ascii_line(const u_char *payload, int len, int offset)
{

    int i;
    int gap;
    const u_char *ch;

    /* offset */
    printf("%05d   ", offset);

    /* hex */
    ch = payload;
    for(i = 0; i < len; i++) {
        printf("%02x ", *ch);
        ch++;
        /* print extra space after 8th byte for visual aid */
        if (i == 7)
            printf(" ");
    }
    /* print space to handle line less than 8 bytes */
    if (len < 8)
        printf(" ");

    /* fill hex gap with spaces if not full line */
    if (len < 16) {
        gap = 16 - len;
        for (i = 0; i < gap; i++) {
            printf("   ");
        }
    }
    printf("   ");

    /* ascii (if printable) */
    ch = payload;
    for(i = 0; i < len; i++) {
        if (isprint(*ch))
            printf("%c", *ch);
        else
            printf(".");
        ch++;
    }

    printf("\n");

return;
}

/*
 * print packet payload data (avoid printing binary data)
 */
void
print_payload(const u_char *payload, int len)
{

    int len_rem = len;
    int line_width = 16;            /* number of bytes per line */
    int line_len;
    int offset = 0;                 /* zero-based offset counter */
    const u_char *ch = payload;

    if (len <= 0)
        return;

    /* data fits on one line */
    if (len <= line_width) {
        print_hex_ascii_line(ch, len, offset);
        return;
    }

    /* data spans multiple lines */
    for ( ;; ) {
        /* compute current line length */
        line_len = line_width % len_rem;
        /* print line */
        print_hex_ascii_line(ch, line_len, offset);
        /* compute total remaining */
        len_rem = len_rem - line_len;
        /* shift pointer to remaining bytes to print */
        ch = ch + line_len;
        /* add offset */
        offset = offset + line_width;
        /* check if we have line width chars or less */
        if (len_rem <= line_width) {
            /* print last line and get out */
            print_hex_ascii_line(ch, len_rem, offset);
            break;
        }
    }

return;
}

/*
 * dissect/print packet
 */
void
got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{

    static int count = 1;                   /* packet counter */

    /* declare pointers to packet headers */
    const struct sniff_ethernet *ethernet;  /* The ethernet header [1] */
    const struct sniff_ip *ip;              /* The IP header */
    const struct sniff_tcp *tcp;            /* The TCP header */
    const char *payload;                    /* Packet payload */

    int size_ip;
    int size_tcp;
    int size_payload;

    printf("\nPacket number %d:\n", count);
    count++;

    /* define ethernet header */
    ethernet = (struct sniff_ethernet*)(packet);

    /* define/compute ip header offset */
    ip = (struct sniff_ip*)(packet + SIZE_ETHERNET);
    size_ip = IP_HL(ip)*4;
    if (size_ip < 20) {
        printf("   * Invalid IP header length: %u bytes\n", size_ip);
        return;
    }

    /* print source and destination IP addresses */
    printf("       From: %s\n", inet_ntoa(ip->ip_src));
    printf("         To: %s\n", inet_ntoa(ip->ip_dst));

    /* determine protocol */    
    switch(ip->ip_p) {
        case IPPROTO_TCP:
            printf("   Protocol: TCP\n");
            break;
        case IPPROTO_UDP:
            printf("   Protocol: UDP\n");
            return;
        case IPPROTO_ICMP:
            printf("   Protocol: ICMP\n");
            return;
        case IPPROTO_IP:
            printf("   Protocol: IP\n");
            return;
        default:
            printf("   Protocol: unknown\n");
            return;
    }

    /*
     *  OK, this packet is TCP.
     */

    /* define/compute tcp header offset */
    tcp = (struct sniff_tcp*)(packet + SIZE_ETHERNET + size_ip);
    size_tcp = TH_OFF(tcp)*4;
    if (size_tcp < 20) {
        printf("   * Invalid TCP header length: %u bytes\n", size_tcp);
        return;
    }

    printf("   Src port: %d\n", ntohs(tcp->th_sport));
    printf("   Dst port: %d\n", ntohs(tcp->th_dport));

    /* define/compute tcp payload (segment) offset */
    payload = (u_char *)(packet + SIZE_ETHERNET + size_ip + size_tcp);

    /* compute tcp payload (segment) size */
    size_payload = ntohs(ip->ip_len) - (size_ip + size_tcp);

    /*
     * Print payload data; it might be binary, so don't just
     * treat it as a string.
     */
    if (size_payload > 0) {
        printf("   Payload (%d bytes):\n", size_payload);
        print_payload(payload, size_payload);
    }

return;
}

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

    char *dev = NULL;           /* capture device name */
    char errbuf[PCAP_ERRBUF_SIZE];      /* error buffer */
    pcap_t *handle;             /* packet capture handle */

    char filter_exp[] = "ip";       /* filter expression [3] */
    struct bpf_program fp;          /* compiled filter program (expression) */
    bpf_u_int32 mask;           /* subnet mask */
    bpf_u_int32 net;            /* ip */
    int num_packets = 10;           /* number of packets to capture */

    print_app_banner();

    /* check for capture device name on command-line */
    if (argc == 2) {
        dev = argv[1];
    }
    else if (argc > 2) {
        fprintf(stderr, "error: unrecognized command-line options\n\n");
        print_app_usage();
        exit(EXIT_FAILURE);
    }
    else {
        /* find a capture device if not specified on command-line */
        dev = pcap_lookupdev(errbuf);
        if (dev == NULL) {
            fprintf(stderr, "Couldn't find default device: %s\n",
                errbuf);
            exit(EXIT_FAILURE);
        }
    }

    /* get network number and mask associated with capture device */
    if (pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
        fprintf(stderr, "Couldn't get netmask for device %s: %s\n",
            dev, errbuf);
        net = 0;
        mask = 0;
    }

    /* print capture info */
    printf("Device: %s\n", dev);
    printf("Number of packets: %d\n", num_packets);
    printf("Filter expression: %s\n", filter_exp);

    /* open capture device */
    handle = pcap_open_live(dev, SNAP_LEN, 1, 1000, errbuf);
    if (handle == NULL) {
        fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);
        exit(EXIT_FAILURE);
    }

    /* make sure we're capturing on an Ethernet device [2] */
    if (pcap_datalink(handle) != DLT_EN10MB) {
        fprintf(stderr, "%s is not an Ethernet\n", dev);
        exit(EXIT_FAILURE);
    }

    /* compile the filter expression */
    if (pcap_compile(handle, &fp, filter_exp, 0, net) == -1) {
        fprintf(stderr, "Couldn't parse filter %s: %s\n",
            filter_exp, pcap_geterr(handle));
        exit(EXIT_FAILURE);
    }

    /* apply the compiled filter */
    if (pcap_setfilter(handle, &fp) == -1) {
        fprintf(stderr, "Couldn't install filter %s: %s\n",
            filter_exp, pcap_geterr(handle));
        exit(EXIT_FAILURE);
    }

    /* now we can set our callback function */
    pcap_loop(handle, num_packets, got_packet, NULL);

    /* cleanup */
    pcap_freecode(&fp);
    pcap_close(handle);

    printf("\nCapture complete.\n");

return 0;
}

但我收到了这个错误：

error: initializer element is not constant
 FILE *f = fopen("test", "w");

Answer 1

如果要将结果写入文件，请移动

FILE *f = fopen("test", "w");

进入您的 main() 函数（也检查返回值，因为该函数可能会失败），如果您希望文件格式为 csv，那么您应该添加扩展名 .csv 以便其他人知道它具有该格式，例如“test.csv”而不是“测试”。将文件指针传递给您需要写入 csv 文件的所有函数。

现在要序列化您收集的内容，并且由于 csv 文件的格式是基于行的，您需要在编写信息之前收集信息（这样更容易）。因此，决定一个结构，其中包含您要在 csv 文件中连续放置的所有信息并填充该结构，在收集信息时创建这些结构的链接列表，然后在完成收集后，遍历列表并在每个结构的 csv 文件中写入一行。

例如

typedef struct CsvRow
{
  char ipLocal[32];
  char ipRemote[32];
  ...
  struct csvRow* next;
} Csvrow;

CsvRow* first;
CsvRow* last;

// collecting
CsvRow* newLine =  malloc(sizeof(CsvRow));
newLine->next = NULL;

if (last == NULL) 
{
  first = last = newLine;
}
else
{
  last->next = newLine;
  last = newLine;
}

// then when you are gathering information just add that in last

strcpy(last->ipLocal, "someip");
..

// at the end of your main function do

FILE* fp = fopen("test.csv", "w");
if (fp == NULL)
{
  fprintf(stderr, "file access denied");
  abort();
}
for (CsvRow* p = first; p != NULL; p = p->next)
{
  fprintf(fp, "%s,%s\n", p->ipLocal, p->ipRemote);
}
fclose(fp);

// free memory
CsvRow* q = first;
while (q != NULL)
{
   CsvRow* next = q->next; 
   free(q);
   q = next;
}

Answer 2

需要将行拆分为打开文件，并声明变量，声明可以原地不动：

FILE *f;

打开必须发生在您的 main() 函数中：

main() 
{
   f = fopen("test.csv", "w");
   ...

然后你可以在任何地方的代码中使用它：

 fprintf(f,"some stuff");

记得在你的程序完成时关闭文件（这将在你的 main() 函数的末尾...

   fclose(f);