How to use fscanf to read lines separated by semicolon [duplicate] - c

Question

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how to identify a field separator from scanf?
(1 answer)
Closed 4 years ago.
For example, I am trying to get the total age from a text file separated by semicolons with the format of Name;Age;Favorite Number
Jack;12;3
Red;21;15
Blue;14;6
I have tried doing something like this.
File *fp;
fp = fopen(in_file,"r");
int sum = 0, age = 0, fav_number = 0;
while (fscanf(fp,"%c %f %f", name, age, fav_number) != EOF) {
fscanf(fp, "%c %f %f", name, age, fav_number);
sum += age;
}
But since it is not separated with space by with semicolon, it wouldn't work. I am not sure how to change it. Any clue on how to do it?

Answer 1

There are few issues with your code. Firstly its recommended to check the return value of fopen() for e.g this
fp = fopen(in_file,"r");
should be
fp = fopen(in_file,"r");
if(fp == NULL) {
/* error handling #TODO */
}
Secondly, the fscanf() arguments are not correct, surely compiler produces the warnings but seems you ignored them. This
while(fscanf(fp,"%c %f %f", &name, &age, &fav_number) != EOF) { /* read the name from file & store into name i.e it should be &name if name is char variable */
fscanf(fp,"%c %f %f", &name, &age, &fav_number);
sum += age;
}
lastly if you want to read the lines separated by semicolon then use %[^;] or use strtok(). Or it's better to read whole line first using fgets() and then use strtok(). To know how strtok() works read the manual page strtok.

Answer 2

There are many issues in your code:
File should be FILE
you should test the return value of fopen()
the format string for fscanf() is incorrect: %c reads just one character, %f requires a pointer to float and you instead provide an int value...
you should compare the return value of fscanf() to the number of expected conversions (3 in your code), not EOF which is only returned at end of file if no conversions were performed.
you call fscanf() twice.
Since you are not interested in the Name and Favorite colour fields, you can just ignore them:
#include <stdio.h>
int main() {
char in_file[] = "test.csv";
FILE *fp;
fp = fopen(in_file, "r");
if (fp != NULL) {
double sum = 0, age = 0;
while (fscanf(fp," %*[^;];%lf;%*lf", &age) == 1) {
sum += age;
}
fclose(fp);
printf("total of ages: %g\n", sum);
}
return 0;
}
Note however that it would be more reliable to read the input file one line at a time and parse it with sscanf():
#include <stdio.h>
int main() {
char buf[256];
char in_file[] = "test.csv";
double sum = 0, age = 0;
FILE *fp;
fp = fopen(in_file, "r");
if (fp == NULL) {
fprintf(stderr, "cannot open input file %s\n", in_file);
exit(1);
}
while (fgets(buf, sizeof buf, fp)) {
if (sscanf(buf,"%*[^;];%lf;%*lf", &age) == 1) {
sum += age;
} else {
fprintf(stderr, "invalid data: %s\n", buf);
fclose(fp);
exit(1);
}
}
fclose(fp);
printf("total of ages: %g\n", sum);
return 0;
}