Here is a small example showing you how to read your file. You can complete it to retrieve the data you need. Then the time axis tutorials on the web will show you how to make a graph with time axis.
{
FILE *f = fopen("measurements.txt","r");
if (f) {
printf("Could not open measurements.txt\n");
return;
}
char line[200];
Int_t i = -1;
int d,m,y;
while (fgets(line,200,f)) {
sscanf(&line[0] ,"%d",&d);
sscanf(&line[3] ,"%d",&m);
sscanf(&line[6] ,"%d",&y);
printf("%d %d %d\n",d,m,y);
}
fclose(f);
}