I am attempting to grab a title from a text file in a way that is completely new to me. My code is set up as follows:
struct sequence
{ char *name;
char *sequence;
int sequencelen;
};
int main(int argc, char *argv[])
{
struct sequence *newseq;
getsequence("test.txt", newseq);
}
void getsequence(const char *file, struct sequence *seq)
{
FILE *fp = fopen(file, "r");
struct sequence *seqptr = malloc(sizeof(*seq));
char c;
if (!fp)
{
exit(1);
}
while ((c = fgetc(fp)) != "\n")
{
if (c == '>')
continue;
strcat(seqptr -> name, c);
}
printf("Name: %s", seqptr -> name); //Expected output: this_is_a_new_sequence_title
}
The structure for the text file is as follows:
>this_is_a_new_sequence_title
Using structs in this way is, like I said, new to me, but seeing how it is another way to use them I would like to know how to do it. I am unsure, however, if I'm using them correctly, especially with regards to the strcat function.
Do I have to dynamically allocate memory for the struct's member variables, and, if so, how would I go about doing that? Or do I just have everything horribly wrong?
You're never allocating memory for the string. So when you call strcat(), the destination string is uninitialized memory, leading to undefined behavior.
Also, the 2nd argument to strcat() is a string, not a character. That's more undefined behavior as the library function interprets the single character as the address of a string.
You need to initialize storage space for sequence when you allocate it. Also, for code like this (dynamic strings) it's good to separate "allocated room" from "string length", and store both.
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