Getting a value next to a number

[da_silvy]

How do I do it?

I have a text file in the form of:

18930 da_silvy
20389 karl_moore
20138 john

(for example)

how could i get it to return da_silvy when 18930 was the value?

[Daok]

You do the same thing that if you were in VB...

Search each line, but it in a String then check for the space:
Here is the idea :

[NUMBER][Space][Name][NewLine]

[da_silvy]

So how would i do that?

[CornedBee]

Have you learned file handling?

// C
#include <stdio.h>

void getName(int index, char *name)
{
  FILE *f = fopen("thefile.dat", "rt");
  while(!feof(f))
  {
    int i;
    char buf[100];
    fscanf("%i %s", &i, buf);
    if(i == index)
    {
      strcpy(name, buf);
      fclose(f);
      return;
    }
  }
  name[0] = '\0';
  fclose(f);
}

// C++
#include <fstream>
#include <string>
using namespace std;

void getName(int index, string &name)
{
  ifstream f("thefile.dat", ios::in | ios::text);
  while(!f.eof())
  {
    int i;
    string str;
    f >> i >> str;
    if(i == index)
    {
      name = str;
      return;
    }
  }
  name.clear();
}

It's really simple.

[CornedBee]

Oh, I can't test that, so I can't guarantee that there are no errors - that's up to you.

[jim mcnamara]

If it's a few thousand records try reading the file into memory
use qsort to sort the array()
use bsearch() to lookup
This would be for a lookup intensive kind of application, like PLU for a scancode.
Otherwise for ten-100 records what CB gave you is fine.
Or for a one-time lookup.

In a lookup intensive app you don't keep hitting the file, you hit it once and get it over with.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
static int last=(-1);
void test(FILE *);
int cmp(void * void *);
int cmp1(void *, void *);
int find(const char *);
static char **list, tmp[256];
FILE *in;
int main(int argc, char *argv[]){
     
     int i;
     test(in=fopen("myfile.txt"));
     while (!feof(in)){       // put text into array
         memset(tmp,0x00,sizeof(tmp);
         if(fgets(tmp,255,in)!=NULL){
              list[++last]=calloc(sizeof(tmp),1);
              strcpy(list[last],tmp);
         }           
     qsort(list,(size_t) last,sizeof(tmp),cmp);  // sort the array
     fclose(in);
     if( find("18960")!= NULL )                 // bsearch lookup
               printf("%s\n",list[find(]);
     for(i=0;i<=last;i++) free(list[i]);             
     return 0;
}

void test(FILE *tst){
    if(tst==NULL){
             perror("Error opening inpout file");
             exit(EXIT_FAILURE);
    }
	return;
}

int cmp(void *s, void *t){
       return( strcmp( (char*)s,(char*)t);
}

char* find(const char *s){
     return (char *) bsearch(s,list,sizeof(tmp),last,cmp1);
}
int cmp1(void *s,void *t){
     return strncmp( ((char*) s, (char*)s, 6);
}

[CornedBee]

Yep right.
In C++ you might want to read the whole file into a map<int, string> container, with the numbers as keys and the names as values. Will REALLY speed up the lookup.

[da_silvy]

Originally posted by CornedBee
Have you learned file handling?

// C
#include <stdio.h>

void getName(int index, char *name)
{
  FILE *f = fopen("thefile.dat", "rt");
  while(!feof(f))
  {
    int i;
    char buf[100];
    fscanf("%i %s", &i, buf);
    if(i == index)
    {
      strcpy(name, buf);
      fclose(f);
      return;
    }
  }
  name[0] = '\0';
  fclose(f);
}

// C++
#include <fstream>
#include <string>
using namespace std;

void getName(int index, string &name)
{
  ifstream f("thefile.dat", ios::in | ios::text);
  while(!f.eof())
  {
    int i;
    string str;
    f >> i >> str;
    if(i == index)
    {
      name = str;
      return;
    }
  }
  name.clear();
}

It's really simple.

thanks for making me feel stupid

i haven't learned C++ before and wrote some different code that didn't seem to work

thanks for your help guys

[CornedBee]

Maybe if I got nothing better to do I'll code my second idea...