CODEWITHSUNDEEP
cfiletextstreamstdin
T.T.T.
T.T.T.

Reputation: 34523

fscanf() error on this text file?

test.txt: 

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
ccccccccccccccccccccccccccccccccccc
The color of the car is blue

code:

FILE *fp;
char var[30];
int result

if( (fp = fopen( "test.txt", "r")) == NULL)  //open for read
    printf("ERROR");


result = fscanf( fp, "The color of the car is %s", &var);

After this executes:

opens file (not NULL and was able to execute an append when testing)
result = 0 //zero- in the case of a matching failure....?
errno = 0;
and var is garbage.

I was expecting fscanf() to match "blue".

How should I correctly get blue into var? Thank You.

Upvotes: 0

Views: 301

Answers (5)

Alam
Alam

Reputation: 1596

Use regex

char p[100];
char q[100];
char r[100];
fscanf(fp, "%[^\n]\n%[^\n]\n%[^\n]\nThe color of the car is %s",p,q,r, &var);

Modify it according to your requirement. I know this is not your actual string.

Upvotes: 1

teppic
teppic

Reputation: 8195

You have another bug here in that if test.txt doesn't exist, your code will go ahead and use fscanf anyway, making your check useless. This would almost certainly cause the program to crash.

Upvotes: 1

jxh
jxh

Reputation: 70382

You have a bug where you are passing in the pointer to an array of char into fscanf, when you should be passing in a pointer to char. It so happens that the address of an array equals the address of the first element of an array, so it works on accident. But, the wrong type is being passed in.

In addition, you want to find the line which provides you with the match, and you seem to want to store "blue" into var. To do this, you should test to see if a line of input matches your scan pattern. You can use fgets to read a line, and use sscanf to scan the line.

while (fgets(buf, sizeof(buf), fp) != 0) {
    result = sscanf(buf, "The color of the car is %s", var);
    if (result == 1) break;
}

sscanf will return how many directives it successfully scanned. In this case, there is the one %s directive.

Doing it this way prevents a scanning error from "jamming" your input parsing. That is, if fscanf returns an error, it will fail to move past the input that caused the error until you call clearerr().

Upvotes: 1

cnicutar
cnicutar

Reputation: 182619

How about using fgets instead:

char *search = "The color of the..";
char *p;
while (fgets(var, SIZE, stdin)) {
    /* Does it have what we want ? */
    if ((p = strstr(var, search)))
        break;
}

if (p)
    p += strlen(str);

Upvotes: 4

user529758
user529758

Reputation:

Fscanf doesn't work like this. It doesn't look around nor scan the string for stuff to match. You have to supply a string exactly matching the format specifier. So you could do stuff like

result = fscanf(fp, "aaaaaaaaaaaaa\nbbbbbbbbbbb\ncccccccccc\nThe color of the car is %s", &var);

to achieve what you want.

Upvotes: 1

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