Why does the second malloc fail in this scenario? - c

Question

I am currently working on a piece of code where we are parsing a file and working with different functions. Through debugging with printf calls, I have found that I am getting a memory error on the second malloc call. What could cause the second malloc to fail in this rough skeleton?
struct example {
char *myChar;
int myInt;
};
struct example *doThing(FILE *file) {
struct example *myToken = (struct example *)malloc(sizeof(struct example));
char buffer[32] = "";
// other stuff
if (strncmp(buffer, "random", 6) == 0) {
strncpy(myToken->myChar, buffer, 6);
myToken->tokenid = 1;
return myToken;
}
return NULL;
}
struct example *doThing2(FILE *file) {
struct example *myOtherToken = (struct example *)malloc(sizeof(struct example));
// other stuff
return myOtherToken;
}
int main() {
FILE *ofp = fopen("thefile.txt", "r");
struct example *token1, *token2;
token1 = doThing(ofp);
token2 = doThing2(ofp);
// other stuff
free(token1);
free(token2);
return 0;
}

Answer 1

You are facing memory leak.
correct your code folowing one of the two samples bellow
and yes, as #Eugene_Sh mentioned, you should allocate memory for myToken->myChar and do not forget to free it before freeing myToken
SAMPLE 1
struct example* doThing(FILE *file) {
char buffer[32] = "";
// other stuff
if (strncmp(buffer, "random", 6) == 0) {
struct example *myToken = (struct example *) malloc(sizeof(struct example));
myToken ->myChar= malloc(7);
strncpy(myToken ->myChar, buffer, 6);
myToken ->myChar[6]=0;
myToken->tokenid = 1;
return myToken;
}
return NULL;
}
SAMPLE 2
struct example* doThing(FILE *file) {
struct example *myToken = (struct example *) malloc(sizeof(struct example));
char buffer[32] = "";
// other stuff
if (strncmp(buffer, "random", 6) == 0) {
myToken ->myChar= malloc(7);
strncpy(myToken ->myChar, buffer, 6);
myToken ->myChar[6]=0;
myToken->tokenid = 1;
return myToken;
}
free(myToken );
return NULL;
}