用c读写文件

Question

i wanna know why my program can't input the numbers of my .txt file them into my array. It reads them but i can't manage to input them into an array for later use. Can anybody help me to understand better the management of reading and writing files in c, please i'm new at this topic, i know i'm supposed to use int instead of chars since my .txt file contains only numbers. But with the functions such as fgets is for chars only i think.

#include <stdio.h>

    int main()
    {
        FILE* file;
        char name[10] = "100.txt";
        char line[10];
        int n;
        char i[5];
        file = fopen(name, "rt");

        if (file == NULL)
        {
            printf("There is no such file!\n");
            return 0;
        }
        for (n=0; n < 100; n++){
        fgets(line, 5, file);
        //puts(line);
        i[n]=line;
        puts(i[n]);
        }
        fclose(file);

        return 0;
    }

Answer 1

if you switch to fscanf you can use int instead of char, and given that you are parsing a text file containing numbers it makes more sense. Assuming your 100.txt has 100 number separated by a whitespace this should work:

int main(int argc, char* argv[])
{
    FILE* file;
    char name[10] = "100.txt";
    char line[10];
    int n;
    int numberArray[100];
    file = fopen(name, "rt");

    if (file == NULL)
    {
        printf("There is no such file!\n");
        return 0;
    }

    for (n=0; n < 100; n++){
        fscanf(file, "%d", &numberArray[n]);
    }
    fclose(file);

    return 0;
}

Here is the link for an explanation of fscanf .

EDIT:

There is another, and more elegant solution, to use fscanf:

while (fscanf(file,"%d",&numberArray[n++]) == 1);

in that way you loop through your text file as long as there are numbers (ie until EOF). Be careful as the program could crash if the count of numbers in the text file is greater than the space allocated for the array.

For writing back to a file:

FILE* fp = fopen( "out_file.txt", "w" ); // Open file for writing
int arrNumSize = sizeof(numberArray) / sizeof(int);
for (int i = 0; i < arrNumSize; i++)
{ 
    fprintf(fp, "%d", numberArray[i] );
}

fclose(fp);