I have a program that reads student names and grades line by line from a .txt file using fgets and a buffer declared as:
char buffer[1024];
Now the file should end with the string "end" on a line all by itself.
How do I tell a while loop to terminate when buffer == "end"?
I tried using strcmp but it segfaults for some reason.
To simply answer your question, strcmp actually is the function you're looking for:
#include <string.h>
if(!strcmp(line, "end\n") || !strcmp(line, "end\r\n"))
break;
or similar should do the trick. Note the ! in front of strcmp as strcmp returns 0 (i.e. false) if the strings match. But I guess you already know that since you've already mentioned strcmp in your question.
On the segfault issue: Are you sure none of the pointers you pass to strcmp are NULL? Most C standard libraries don't do any error checking here and will run into segfaults when trying to read the memory at *(0).
Another possible issue that pops into my mind is that using strcmp will of course only work if you've already split your buffer into an array of single strings. strtok_r is probably most suited for this task (Altough quite tricky to use).
\r is unnecessary; if you read in text mode, then OS-specific line endings are translated to '\n'.
fopen) and it specifically says in the standard that r and rb are identical modes.'\n' to terminate lines. On Windows, for example, "r" and "rb" are distinct; "r" translates \r\n to \n, and "rb" doesn't. Things get tricky when you're reading files in a foreign text format, but I don't think the OP needs to worry about that..txt extension smells like Windows since its rare for text files to have any sort of extension on POSIX systems, which may be what the OP is using. Without knowing the file format or the host environment it is safer to search for both \n and \r\n.Why not just use formatted IO when the format of the text in the file is fixed and use !EOF for looping?
For example:
while(fp!=EOF)
{ fscanf(fp,"%s %s %d",name,grades, &marks);
printf("Name: %s\tGrade: %s\t Marks: %d\n",name,grade,marks);
}
This would automatically detect the end of file, which would also remove the condition of having a string 'end' in the text file.
fp != EOF is correct? Also, read the manual or documentation for fscanf().char *fgets(char *restrict s, int n, FILE *restrict stream);
The fgets() function shall read bytes from stream into the array pointed to by s, until n-1 bytes are read, or a is read and transferred to s, or an end-of-file condition is encountered. The string is then terminated with a null byte.
so, when you read string "end", the element in buffer should be {'e', 'n', 'd', '\n', '\0'}, you can using strcmp as follows:
size_t len = strlen(buffer);
if (buffer[len - 1] == '\n')
{
buffer[len - 1] == '\0';
}
if (strcmp(buffer, "end") == 0)
{
//end
}
or
if (strncmp(buffer, "end", 3) == 0)
{
//end
}
Using strncmp(buffer, "end", 3) to compare the first three characters along with if(3 == strlen(buffer) to make sure end does not start the line, should solve the problem.
'\n'. It's better to deal with the '\n' directly. Using strncmp(line, "end", 3") also creates false positive results for lines starting with \"end"\.
strncmp(buffer, "end", 3) will incorrectly indicate a match on a line consisting of "endurance".
strcmpis the right function to use, it must be something else.strcmpsegfaults rather than avoiding the issue.