How to read from a sequential txt file

[hen_ry]

Hi,

I want to read in two char[] and a int from txt file then print them to the screen.

The problem is when output to the screen, the space is missing and get extra iput at the end of file.

The input file (e:\\text.txt) consists of

Hong Kong, China, 1\n
Tokyo, Japan, 2\n
Szhen, China, 3\n

#include <stdio.h>

int main()
{
    FILE *fp=fopen("e:\\text.txt", "r");

    char city[256];         /*city name: 256 long */
    char country[256];  /*country name: 256 long*/
    int  pop;                  /*Country population*/

    while(!feof(fp))
    {
        fscanf(fp, "%s%s%d", city,country, &pop);

        printf("%s%s%d",city,country, pop);
    }

    fclose(fp);

    getchar();
    return 0;
}

---------------------------------
Output
HongKong,256China,1256Tokyo,Japan,2Szhen,China,3Szhen,China,3

--------------------------------

I have noted
1. number 256 add to it, does it mean a space?
2. why Szhen,China,3 input twice?

--------------------------------

Question
1. Does the output of sequential file output always look like
data1data2..........datan
If yes

2. How to print add a new line to the input int, ie. after input 1, 2, 3
3. How to get rid of extra input?

---------------------------------------------------
I have seen on some tutorial, they use %[^\n] to delimit the input, what does it mean?
------------------------------

Can anyone please help.
Thanks
Henry

[Salem]

Read the FAQ on why using feof() to control a loop is bad (for this very reason).

[hk_mp5kpdw]

The problem is when output to the screen, the space is missing

...

2. How to print add a new line to the input int, ie. after input 1, 2, 3

The program prints what you tell it to print. If the output is not what you expect, then you must deal with that. In these cases, your print function does not contain spaces or a newline so there is no space between the city/country/pop values and no newline at the end of the pop value. You must put those there:

printf("%s %s %d\n",city,country, pop);
          ^  ^ - Note spaces here

I have seen on some tutorial, they use %[^\n] to delimit the input, what does it mean?

In this case it means to read up to (but not including) the newline character. In your case, given the expected input you've described, I'd make the fscanf line like this:

fscanf(fp, " %[^,], %[^,], %d", city,country, &pop)

2. why Szhen,China,3 input twice?

This relates to what Salem has mentioned. Avoid using feof to control you loops. It would be better to use the return result from the fscanf call in place of the feof call to control this loop. The fscanf function returns the number of values it successfully converted/stored. In your case, since you're reading in 3 values, you'd expect the return value to be equal to 3. You can test this in the loop instead of the feof call. The reason this is getting output twice is that the end-of-file flag does not get set to true until after an attempt is made to read past the end of the file. When you've read the last line in the file, feof still returns false and you wind up going through the loop another time in error trying to process data that isn't there. The read operation fails - which this time sets the end-of-file flag to true - and the data that was read in from the previous loop is still in your variables and gets output a second time.

[edit]Understand the difference between input/output. You seem to be confusing them here many times.[/edit]

[hen_ry]

Hi,

Thanks for your help. The result print correctly.

Henry

[c.user]

    fscanf(fp, "%255[^,]%*c%255[^,]%*c%10d\t", city, country, &pop);

it is for limitation of a data and for clearing space character after line when you use a %[^,] format specifier

[hen_ry]

Hi,

Thank you for your help, problem solve.

Now I want to ask user to enter a city name to see if in the file. If it is print its population.

The problem is there are two city name with similar length, my program can't disguish between the two cities and print them on screen.

I have use if(strncmp(city, cityName, strlen(cityName)==0) to compare the string.

--------------------------------
Part of input file:

Abidjan,C?te d'Ivoir
          *
          *

St. Louis,USA,2825000
St. Petersburg,Russia,4775000
Stockholm,Sweden,1910000

          *
          *

----------------------------------

My code

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

/*Purpose: get city name from user
           See if cityname is in the file.
           If it is print population

   Problem occur when type in a city there are two cities with similar name
   it will print both out.

   e.g INPUT : St. Louis
       OUTPUT: St. Petersburg
*/

int main()
{
    FILE *fp=fopen("e:\\city.txt", "r");

    char city[256];
    char country[256];
    int  pop;

    char cityName[256];
    int i;

    printf("Which city do you want to search for? ");
    scanf("%s", cityName);

    /*Read three items per line*/
    while(fscanf(fp," %[^,], %[^,], %d", city, country, &pop)==3)
    {
           /*Compare the whole cityName[] with city[] in the file.*/

           if(strncmp(city, cityName,strlen(cityName))==0)

           {
               printf("%s %s %d\n",city, country, pop);
           }
    }

    fclose(fp);

    fflush(stdin);
    getchar();
    return 0;
}

---------------
Is my logic correct?

Are there any method to solve the problem?

-----------------------
OUTPUT

Which city do you want to search for? St. Louis
St. Louis USA 2825000
St. Petersburg Russia 4775000

Thanks
Henry

[hk_mp5kpdw]

printf("Which city do you want to search for? ");
scanf("%s", cityName);

Using scanf with a straight %s format specifier will mean that you'll only store up to the first whitespace into cityName. If you type in "St. Louis" for example, only the "St." part is going to be stored because of the space between the two parts. This plus the way you do the comparison based on the length of the cityName string instead of the city string, means that you are finding anything in the file that begins with "St.". To deal with this, your read of the city to search for must include everything up to the newline so you get "St. Louis" instead of just "St.". Using something like fgets instead and then removing the trailing newline from the read string before doing you comparison would work... alternately, you could use something like scanf("%255[^\n]%*c",city) instead which would read up to the newline. The %*c will eat and ignore the newline so that your later getchar call will work by pausing things on screen. This would then get the whole city name "St. Louis" instead of just "St." and the comparison should then work.

fflush(stdin);

fflush is undefined for input streams, it should only be used for output streams. Read the FAQ for the "why".

[c.user]

%255[^,] will not clear spaces before the name (they will be read as a part of a name, so I suggest you two-steps read, one for read ...,...,... and second for read names without spaces before them)

[hen_ry]

Hi,

Thanks all for your help, problem solved.

My modified code.

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

int main()
{
    FILE *fp=fopen("e:\\city.txt", "r");

    char city[256];
    char country[256];
    int  pop;

    char cityName[256];
    int i;

    printf("Which city do you want to search for? ");
    scanf("%[^\n]", cityName);

    /*Read three items per line, i.e. city name, country name, population*/
    while(fscanf(fp," %[^,], %[^,], %d", city, country, &pop)==3)
    {
           if(strncmp(city, cityName,strlen(cityName))==0)
           {
               printf("%s %s %d\n",city, country, pop);
           }
    }

    fclose(fp);

    fflush(stdin);
    getchar();
    return 0;
}

Sample run

Sample run 00

Which city do you want to search for? A

Abidjan C?te d'Ivoire 4225000
Accra Ghana 3350000
Adana Turkey 1360000
Addis Abeba Ethiopia 3100000
Adelaide Australia 1150000
Agra India 1700000
Ahmedabad India 5650000
Ahvaz Iran 1030000
Aleppo Syria 2850000
Alexandria Egypt 5100000
Algiers Algeria 4275000
Allahabad India 1230000
Alma-Ata Kazakhstan 1230000
Amman Jordan 2850000
Amritsar India 1270000
Amsterdam Netherlands 1910000
Ankara Turkey 3875000
Anshan China 2200000
Antananarivo Madagascar 1760000
Antwerp Belgium 1110000
Arbil Iraq 1240000
Asansol India 1580000
Asunci?n Paraguay 2025000
Athens Greece 3725000
Atlanta USA 5500000
Auckland New Zealand 1260000
Austin USA 1560000

------------------------------------------------------
Sample run 01

Which city do you want to search for? St.

St. Louis USA 2825000
St. Petersburg Russia 4775000

---------------------------------------------------------
Sample run 02

Which city do you want to search for? St. L

St. Louis USA 2825000

--------------------------------------------------------
Sample run 03

Which city do you want to search for? St. Louis

St. Louis USA 2825000

Henry