CODEWITHSUNDEEP
cstringscanf
Rob L
Rob L

Reputation: 3303

Why isn't fscanf() storing this string in this pointer?

Ok, so I am having trouble reading in the string names and storing them in my struct array of type student. The age field is an int and the gpa field is a double and those worked fine. Then when I added the name to be read I started running into issues. How can I successfully read in a name and store it in the student.name field? The code below crashes and I am not sure why. I am new in C so please tell me if there is a better way to do this. Thank you in advance. Oh and the name is consecutive letters with no spaces between characters.

typedef struct student{
     char *name; int age; double gpa;
}student; 

void read(char *filename) {
File *file = fopen(filename,"r");  
if(!file) return; 
student *students = malloc(sizeof(student)*100); 
int num_students = 10; //for example
int i; 
for (i=0;i<num_students;i++) {

    char *n = malloc(MAXLENGTH); 
    fscanf(file,"%s %i %lf", n,&students[i].age,&students[i].gpa); //<---runtime error occurs here
    strcpy(students[i].name,n);
    free(n);
} 

/*code here to do stuff with the array*/
free(students); 
fclosef(file); 
}

Upvotes: 0

Views: 323

Answers (3)

tesseract
tesseract

Reputation: 901

int n =0;
for (i=0;i<num_students;i++) {

char *n = malloc(MAXLENGTH); 
n = fscanf(file,"%s %i %lf", n,&students[i].age,&students[i].gpa);
if(n!= 3 || n = EOF){
    printf("invald input..");
}
students[i].name = malloc(strlen(n) +1);
if(student[i].name != NULL){
    strcpy(students[i].name,n);
}
free(n);
}

man fscanf

Upon successful completion, these functions return the number of successfully matched and assigned input items; this number can be 0 in the event of an early matching failure. If the input ends before the first matching failure or conversion, EOF is returned. If a read error occurs the error indicator for the stream is set, EOF is
returned, and errno is set to indicate the error.

Upvotes: 1

Abend
Abend

Reputation: 589

Your problem is that the "string" into the file that you want to store into n array does not have null terminator. So %s does not work fine into the fscanf(). Try another option to that, as treat it as a cvs file.

Upvotes: 0

Ahmed Hamdy
Ahmed Hamdy

Reputation: 2897

Try to replace this line strcpy(students[i].name,n); with students[i].name = strdup(n);

I use strdup to allocate enough memory to hold the string, if you tried = it will work but will make name as read only! strcpy() will work too
Here you are reference for strdup use: strdup() - what does it do in C?

Also I don't see you allocating memory for students[i].name

Upvotes: 1

Related Questions