Using fopen with input filenames in C

问题

At some point in my code, I want to read a name for a file that I will be creating (and/or editing) and I've come up with the following:

FILE *fp;
char filename[15];
fgets(filename, 15, stdin);
fp = fopen(filename, "a");
fprintf(fp, "some stuff goes here");
fclose(fp);

Even though that does compile and run, it does not create (or open, if I manually create it) the file specified by filename.
What would you suggest?

回答1:

fgets() stores the newline character read from stdin after reading a line of input. You need to strip it manually, e.g.

size_t len = strlen(filename);
if (len > 0 && filename[len - 1] == '\n')
    filename[len - 1] = '\0';

You should also check that fopen() doesn't return NULL, which it will do if it was unable to open the file. I think using fprintf with a NULL file pointer is undefined behaviour.

回答2:

Usually(but not always), fgets() will give you an extra '\n' appending the inputted string, because

A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.

_{Reference: http://www.cplusplus.com/reference/cstdio/fgets/}

To get rid of that '\n' using minimal code:

fgets(filename, 15, stdin);
filename[strcspn(filename, "\n")] = '\0';

回答3:

You need to declare filename[16] to be able to use 15 characters, you need space for the terminating zero.

回答4:

Since fgets will read string util an EOF or a newline, and if a newline is read, it is stored into the buffer. That means you have to manually trim the ending newline if any. I'd suggest use fscanf instead, it won't add the newline to the buffer:

char filename[15];
int ret = fscanf(stdin, "%s", filename);
if (ret != 1) { // handle input error }
fp = fopen(filename, "a");

来源：https://stackoverflow.com/questions/36635063/using-fopen-with-input-filenames-in-c

标签

string

file

fopen