Read a string and get it in (int) in C

Question

Can you help me? I have a string 23;56;36.6;run in a txt file.Then I am reading this string in order to use it for some work: I would like to take this values from a string, then compare them with some values in a code and output my result in console. I think,I should use atoi() function that make my string in numbers, for picking out , I am using strtok(). But how correctly should I record my tokens in loop while and the last token is a type of char. How can I do this work?

CODE:

void printInfo(int note)
{
    int i;
    FILE *out;
    char str[250];
    char sp[10]=";";
    char *istr;


    if ((out =fopen("test.txt","r"))==NULL)
        printf("Error open, file\n");
    else
    {
        for (i=0;i<note;i++)
        {
            fgets(str,250,out);
            istr=strtok(str,sp);
            while (istr != NULL)
            {
                printf("%d\n",atoi(istr));
                istr=strtok(NULL,sp);
                // I think, I need to create a variable for recording my values.
            }
        }
    }
   fclose(out);
}

You can convert strings to integer (or floats) with `sscanf`. — Marco, Feb 10 '17 at 18:49
I would say the easiest solution is simply: `sscanf("23;56;36.6;run", "%f;%f;%f;", &n[0], &n[1], &n[2]);` — Marco, Feb 10 '17 at 18:50

Marco · Accepted Answer · 2017-02-10T21:28:47.263

1

I would use sscanf to convert the string to the three floats:

#include <stdio.h>  // sscanf
#include <stdlib.h> // EXIT_SUCCESS
#include <string.h> // memset

int main(void) {
    const char *input = "23;56;36.6;run";
    int i;
    float numbers[3]  = {0, 0, 0};
    char buf[10];
    int nElementsRead;

    // init buf
    memset(buf, 0, sizeof(buf));

    // sscanf returns the number of read elements
    // or EOF on error
    nElementsRead = sscanf(input, "%f;%f;%f;%9s", &numbers[0], &numbers[1], &numbers[2], buf);

    if (nElementsRead == 4) {
        printf("Successfully read %d elements\n", nElementsRead);

        for (i = 0; i < 3; ++i) {
            printf("number[%d]: %f\n", i, numbers[i]);
        }

        printf("Buffer is: %s\n", buf);
    } else {
        printf("Something went wrong!");

        return EXIT_FAILURE;
    }

    return EXIT_SUCCESS;
}

edited Feb 10 '17 at 21:28

answered Feb 10 '17 at 18:55

Marco

7,007
2
19
49

thank you, but how should it go with `char` the last token? – Nikita Gusev Feb 10 '17 at 19:00
You can read chars with `sscanf` as well: `sscanf(input, "%10s", buf);` means you want to scan a string that is max. 10 chars long. – Marco Feb 10 '17 at 19:02
`if (nElementsRead == 4)` is better than `if (nElementsRead != EOF)` here. `buf[9] = 0;` serve no value. – chux - Reinstate Monica Feb 10 '17 at 20:53
@chux are strings always null terminated by sscanf? – Marco Feb 10 '17 at 20:54
3

Yes, `sscanf()` appends a null character, if at least 1 character was scanned into `buf`. In C a _string_ always has a null terminator - else it is not a _string_, just an array of characters. – chux - Reinstate Monica Feb 10 '17 at 21:25
2

BTW: `"%f;%f;%f;%10s"` --> `"%f;%f;%f;%9s"`. `9` is the max _width_, the max number of characters to save into `buf`. Since a null character is appended, code should only save up to 9 characters into `buf[10]`. – chux - Reinstate Monica Feb 10 '17 at 21:28

score 0 · Answer 2 · answered Feb 10 '17 at 19:36

Another solution, using comparable records:

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

typedef struct MyRecord_s {
   int   f1;
   int   f2;
   float f3;
   char  f4[10];

} MyRecord;

static int MyRecordInit( MyRecord * out, char * line ) {
   if( out == NULL ) {
      return 0;
   }
   char * f1 = strtok( line, ";" );
   char * f2 = strtok( NULL, ";" );
   char * f3 = strtok( NULL, ";" );
   char * f4 = strtok( NULL, ";" );
   if( f1 && f2 && f3 && f4 ) {
      char * err = NULL;
      out->f1 = strtol( f1, &err, 10 );
      if( err && *err ) {
         return 0;
      }
      out->f2 = strtol( f1, &err, 10 );
      if( err && *err ) {
         return 0;
      }
      out->f3 = strtof( f1, &err );
      if( err && *err ) {
         return 0;
      }
      strncpy( out->f4, f4, 10 );
      out->f4[9] = '\0';
      return 1;
   }
   return 0;
}

int MyRecordCmp( const MyRecord * r1, const MyRecord * r2 ) {
   int diff = r1->f1 - r1->f2;
   if( diff ) {
      return diff;
   }
   diff = r1->f2 - r2->f2;
   if( diff ) {
      return diff;
   }
   float d = r1->f3 - r2->f3;
   if( d > 0.000001 ) {
      return +1;
   }
   if( d < -0.000001 ) {
      return -1;
   }
   return strcmp( r1->f4, r2->f4 );
}

int main() {
   char line1[] = "23;56;36.6;run";
   char line2[] = "24;57;37.6;stop";
   MyRecord r1, r2;
   if( MyRecordInit( &r1, line1 ) && MyRecordInit( &r2, line2 )) {
      printf( "cmp: %d\n", MyRecordCmp( &r1, &r2 ));
   }
   return 0;
}

Read a string and get it in (int) in C

2 Answers2