Read header of PPM file only using getchar()

Question

I need to read a PPM file but I'm limited to only using getchar() but I'm running into trouble ignoring whitespaces.

I'm using num=num*10+(ch-48); to read the height and width but don't know how to read them all at once while ignoring spaces and '\n' or cmets.

I use this to read the magic number:

int magic;
while(magic==0){
if (getchar()=='P')     //MAGIC NUMBER
magic=getchar()-48;
}
printf("%d\\n",magic);

i used this function to read the height and width which works only when the data in the header is seperated only by '\n'

int getinteger(int base)
{ char ch;
int val = 0;
while ((ch = getchar()) != '\\n' && (ch = getchar()) != '\\t' && (ch = getchar()) != ' ')
if (ch \>= '0' && ch \<= '0'+base-1)
val = base\*val + (ch-'0');
else
return ERROR;
return val;
}

this is the part in main()

height=getinteger(10);
    while(height==-1){
        height=getinteger(10);
    }

Answer 1

Something like this?

int getinteger(int base) {
    char ch = getchar();
    if (ch == EOF || ch == '
' || ch == '	' || ch == ' ')
        return getinteger(base); // continue, skip symbols

    if (ch < '0' || ch > '0' + base - 1)
        return ERROR;

    int val = 0;
    do {
        val = base * val + (ch - '0');
        ch = getchar();
    } while (ch >= '0' && ch <= '0' + base - 1);
    return val;
}

int main() {
    // dunno what's before
    int magic = 0;
    while (magic == 0) {
        if (getchar() == 'P') // MAGIC NUMBER
            magic = getchar() - '0';
    }
    printf("magic = %d
", magic);
    int height = getinteger(10);
    int width = getinteger(10);
    printf("height = %d, width = %d
", height, width);
    // dunno what's after
}

Result:

$ echo "   
  P3   34  	  56" | ./a.out

magic = 3
height = 34, width = 56