Why is the "strcat" function not working?
I am trying to concatenate arrays from a struct using strcat
. My code looks like this:
int main(){
//Implementation of Search table Tree
struct searchTable
{
char first[10];
int first_id;
char second[10];
int second_id;
char third[10];
int third_id;
char fourth[10];
int fourth_id;
char fifth[10];
int fifth_id;
}input[5]= {
{"ABC", 101},
{"CAB",102},
{"ACB",103},
{"AAC",104},
{"CCB",105}
};
char join[100]={0};
strcat(join, input[0].first);
strcat(join, input[1].second);
strcat(join, input[2].third);
strcat(join, input[3].fourth);
strcat(join, input[4].fifth);
printf("%s", join);
Here's the output instead of giving me
ABCCABACBAACCCB
gives me just
ABC
Can anyone tell me what I am doing wrong?
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Instead, write
strcat(join, input[0].first);
strcat(join, input[1].first);
strcat(join, input[2].first);
strcat(join, input[3].first);
strcat(join, input[4].first);
Using these initializers
//...
}input[5]= {
{"ABC", 101},
{"CAB",102},
{"ACB",103},
{"AAC",104},
{"CCB",105}
};
you have explicitly initialized only the first two data elements of each array element, which is first
and first_id
. All other data items were initialized to zero.
If you want to use your assertions exactly with strcat
strcat(join, input[0].first);
strcat(join, input[1].second);
strcat(join, input[2].third);
strcat(join, input[3].fourth);
strcat(join, input[4].fifth);
then initialize the array like this
struct searchTable
{
char first[10];
int first_id;
char second[10];
int second_id;
char third[10];
int third_id;
char fourth[10];
int fourth_id;
char fifth[10];
int fifth_id;
}input[5]= {
{ .first = "ABC", .first_id = 101 },
{ .second = "CAB", .second_id = 102 },
{ .third = "ACB", .third_id = 103 },
{ .fourth = "AAC", .fourth_id = 104 },
{ .fifth = "CCB", .fifth_id = 105 }
};
In this case, the output will look like
ABCCABACBAACCCB
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The problem is that on initialization during definition, you only initialize the first two member variables of each element input[n]
(check the number of initializers provided). So later, doing
strcat(join, input[1].second);
strcat(join, input[2].third);
strcat(join, input[3].fourth);
strcat(join, input[4].fifth);
all member variables second
, third
, fourth
and fifth
elements input[n]
are initialized to 0
, or a null pointer, since the definition of the array is global.
The output is correct and this is the expected output for this code.
Having said that, the recommended signature main()
is equal to int main(int argc, char *argv[])
or at least int main(void)
.
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You are declared a ten-member structure
struct searchTable
{
char first[10];
int first_id;
char second[10];
int second_id;
char third[10];
int third_id;
char fourth[10];
int fourth_id;
char fifth[10];
int fifth_id;
}
When assigning a value, you are specifying two values, so the first two values will be assigned. The rest of the variables will be empty.
strcat(join, input[1].second);
strcat(join, input[2].third);
strcat(join, input[3].fourth);
strcat(join, input[4].fifth);
If you do this, you will receive this output as expected.
strcat(join, input[0].first);
strcat(join, input[1].first);
strcat(join, input[2].first);
strcat(join, input[3].first);
strcat(join, input[4].first);
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Your initializer doesn't cover all members struct searchTable
, only the first two elements for each element in the array input
. The rest are zero-initialized implicitly. Thus:
strcat(join, input[1].second);
strcat(join, input[2].third);
...
is concatenated with empty strings, as they are all treated as zero-length, because they start with a null character '\0'
(or NUL
in ASCII). In other words:
strlen(input[1].second) == 0
strlen(input[2].third) == 0
...
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