从txt文件读取并输入到C中的数组

Question

I have my txt file

4  
110  
220  
112  
335 

4 is the number of lines and 4*3 the number of int. I have to read "4" then read the remaining and input them into an array

This is what I have

void main(){ 
    int a,n;    
    int i=0,j=0,k[30]; //
    int *N;

    FILE *fp = fopen("test.txt", "r");  
    if(fscanf(fp, "%d", &a) != 1) { //
       // something's wrong 
    }

    n=3*a; //3*a numbers in the file
    N = malloc(3 * a * sizeof(int)); 
    for(i = 0; i <n;++i) {
       int result=fscanf(fp, "%d", &N[i] );  
    }   
    fclose(fp);  
    for(j=0;j<3*a;j++){  
       k[j]=N[j]; 
    }

    printf("%d",k[0]);
 }

When I print k[0] it was supposed to print "1" but instead the whole line "110" is printed

Is there any other way to do this???

Answer 1

The format specifier %d does not specify a length, so fscanf will read as many digits as it can; this is why you get 110 instead of just 1.

If you specify a length, like %1d , it will only read as many digits as you tell it to:

for(i = 0; i <n;++i) {
   int result=fscanf(fp, "%1d", &N[i] );  
}   

Answer 2

When you use fscanf with %d format parameter, it retrieves an integer type from the file. Since 110 and the others are all integers, it will directly fetch 110 from file.

So you can either use fscanf with %d parameters in a loop which iterates for a times, or if you want to get it character by character, you can use fscanf with %c parameter but it needs much more effort. So, you should use fscanf with %d parameter and fetch all digits from it by a loop for every number.

Answer 3

The fscanf(fp, "%d", &N[i] ) will catch a number and not a digit. So

fscanf(fp, "%d", &N[0] )  //will catch 110
fscanf(fp, "%d", &N[1] )  //will catch 220
...

If you want to catch digits in your array you have to use the following code:

for(i = 0; i <n;++i) {
    int result=fscanf(fp, "%c", &N[i] );
    if (isdigit (N[i])) N[i]-='0';
    else i--;
}