How to read input from stdin until EOF read line by line with each line containing four space separated integers in C

Question

How to read input from stdin until EOF read line by line with each line containing four space separated integers in C. It could be inputted by commands like this:

$ echo 1 2 3 4 | ./myProgram

or

$ cat file.txt
1 2 3 4
0 -3 2 -4

$ ./myProgram < file.txt
"This is where it would output my calculations"

Then I want to save the individual integers to int variables.

char strCoordinates[101];
    char *ptr;
    int coordinates[4];
    long int tempCoordinates;
    while(scanf("%s", strCoordinates) != EOF) {
        tempCoordinates = strtol(strCoordinates, &ptr, 10);
        int lastDigit = 0;
        for (int x = 4; x >= 4; x--) {
            lastDigit = tempCoordinates % 10;
            coordinates[x] = lastDigit;
            tempCoordinates = (tempCoordinates - lastDigit) / 10;
            }
    }

This is what I was trying but it seems way to complicated . . .

Any help would be greatly apprecated. Not sure whether to use scanf(), sscanf(), fscanf(), gets()

How about `while(scanf("%100[^\n]%*c", strCoordinates) != EOF)` @BLUEPIXY — joshuatvernon, Mar 29 '15 at 09:30

score 2 · Accepted Answer · answered Mar 29 '15 at 09:35

2

Examples of One way

char strCoordinates[101];
char *ptr;
int coordinates[4];
while(fgets(strCoordinates, sizeof(strCoordinates), stdin) != NULL) {
    char *s = strCoordinates;
    for (int x = 0; x < 4; x++) {
        coordinates[x] = strtol(s, &ptr, 10);
        s = ptr;
    }
    printf("%d,%d,%d,%d\n", coordinates[0],coordinates[1],coordinates[2],coordinates[3]);
}

answered Mar 29 '15 at 09:35

BLUEPIXY

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Why use `&ptr` rather than `&s`? And if you do want `ptr`, why not make it local to the `for` loop? – The Archetypal Paul Mar 29 '15 at 09:41
@Paul 1) Probably not be a problem, but two pointers is `restrict`. `long strtol( const char * restrict nptr, char ** restrict endptr, int base);`. 2) Not mean much. Because it is part of the code impact on the other is small is to define most recently to use a variable that I have added. – BLUEPIXY Mar 29 '15 at 10:06
1

Those restricts just say that nptr and endptr don't point to the same array. Since &s definitely not in the same array as the string s points to, that's OK even if you do pass &s – The Archetypal Paul Mar 29 '15 at 15:31

How to read input from stdin until EOF read line by line with each line containing four space separated integers in C

1 Answers1