c - 当某些字段为空时，如何使用 sscanf 和 scanset 以逗号分隔的字符串提取字段

Question

如果所有字段都已填充，我可以使用 sscanf(见下文)以逗号分隔格式提取字段。但是，如果一个字段是空白的，那么只会填充空白字段。有什么方法可以继续，忽略空白字段的问题，以便填充后续字段吗？

#include <stdio.h>

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

   char* s = "Apple,Pear,Potato,11";

   char fruit1[10];
   char fruit2[10];
   char vegetable[10];
   int size;


   int num = sscanf(s, "%20[^,],%20[^,],%20[^,],%d", fruit1, fruit2, vegetable, &size);
   if (num == 4) {
      printf("This record contains 4 items\n");
      printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", fruit1, fruit2, vegetable, size);
   }
   else {
      printf("This record does not contain 4 items\n");
   }


   // but here it fails - blank vegetable
   char* t = "Plum,Orange,,12";
   num = sscanf(t, "%20[^,],%20[^,],%20[^,],%d", fruit1, fruit2, vegetable, &size);

   if (num == 4) {
      printf("This record contains 4 items\n");
      printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", fruit1, fruit2, vegetable, size);
   }
   else {
      printf("This record does not contain 4 items\n");
   }

   return 0;
}


/*
Prints:
This record contains 4 items
first fruit: Apple, second fruit: Pear, vegetable: Potato, size = 11
This record does not contain 4 items
*/

Answer 1

您可以使用strchr构建您自己的扫描函数，注意scan将,替换为\0原始字符串，所以如果你想标记一个字符串文字(只读)你需要一个中间缓冲区:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *scan(char **pp, char c)
{
    char *s = *pp, *p;

    p = strchr(*pp, c);
    if (p) *p++ = '\0';
    *pp = p;
    return s;
}

int main(void)
{
    char s1[] = "Apple,Pear,Potato,11";
    char s2[] = "Plum,Orange,,12";
    char fruit1[10];
    char fruit2[10];
    char vegetable[10];
    int size;
    char *p;

    p = s1;
    strcpy(fruit1, scan(&p, ','));
    strcpy(fruit2, scan(&p, ','));
    strcpy(vegetable, scan(&p, ','));
    size = strtol(scan(&p, ','), NULL, 10);
    printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", fruit1, fruit2, vegetable, size);

    p = s2;
    strcpy(fruit1, scan(&p, ','));
    strcpy(fruit2, scan(&p, ','));
    strcpy(vegetable, scan(&p, ','));
    size = strtol(scan(&p, ','), NULL, 10);
    printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", fruit1, fruit2, vegetable, size);

    return 0;
}

您可以使用指针简化您的代码:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *scan(char **pp, char c)
{
    char *s = *pp, *p;

    p = strchr(*pp, c);
    if (p) *p++ = '\0';
    *pp = p;
    return s;
}

int main(void)
{
    char s1[] = "Apple,Pear,Potato,11";
    char s2[] = "Plum,Orange,,12";
    char *v[4], *p;
    int i;

    p = s1;
    for (i = 0; i < 4; i++) v[i] = scan(&p, ',');
    printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", v[0], v[1], v[2], atoi(v[3]));

    p = s2;
    for (i = 0; i < 4; i++) v[i] = scan(&p, ',');
    printf("first fruit: %s, second fruit: %s, vegetable: %s, size = %d\n", v[0], v[1], v[2], atoi(v[3]));

    return 0;
}