Reputation: 31
Here is a weird problem:
token = strtok(NULL, s);
printf(" %s\n", token); // these two lines can read the token and print
However!
token = strtok(NULL, s);
printf("%s\n", token); // these two lines give me a segmentation fault
Idk whats happened, because I just add a space before %s\n, and I can see the value of token.
my code:
int main() {
FILE *bi;
struct _record buffer;
const char s[2] = ",";
char str[1000];
const char *token;
bi = fopen(DATABASENAME, "wb+");
/*get strings from input, and devides it into seperate struct*/
while(fgets(str, sizeof(str), stdin)!= NULL) {
printf("%s\n", str); // can print string line by line
token = strtok(str, s);
strcpy(buffer.id, token);
printf("%s\n", buffer.id); //can print the value in the struct
while(token != NULL){
token = strtok(NULL, s);
printf("%s\n", token); // problem starts here
/*strcpy(buffer.lname, token);
printf("%s\n", buffer.lname); // cant do anything with token */
}}
fclose(bi);
return 1;}
Here is the example of string I read from stdin and after parsed(I just tried to strtok the first two elements to see if it works):
<15322101,MOZNETT,JOSE,n/a,n/a,2/23/1943,MALE,824-75-8088,42 SMITH AVENUE,n/a,11706,n/a,n/a,BAYSHORE,NY,518-215-5848,n/a,n/a,n/a
<
< 15322101
< MOZNETT
Upvotes: 1
Views: 151
Reputation: 1865
Your problem reduces to the following question What is the behavior of printing NULL with printf's %s specifier? .
In short NULL as an argument to a printf("%s")
is undefined. So you need to check for NULL as suggested by @kninnug
You need to change you printf as follows:
token = strtok(NULL, s);
if (token != NULL) printf("%s\n", token);
Or else
printf ("%s\n", token == NULL ? "" : token);
Upvotes: 1
Reputation: 41
In the first version your compiler transforms printf()
into a
puts()
and puts does not allow null pointers, because internally
invokes the strlen()
to determine the lenght of the string.
In the case of the second version you add a space in front of format
specifier. This makes it impossible for the compiler to call puts
without appending this two string together. So it invokes the actual
printf() function, which can handle NULL
pointers. And your code
works.
Upvotes: 2