"Invalid argument" when creating a file - c

Question

Could you help me with the creation of a text file as right now the *fp pointer to the file is returning NULL to the function fopen ?
Using the library errno.h and extern int errno I get "Value of errno: 22".
if (!fp)perror("fopen") gives me "Error opening file: Invalid argument".
In my main function I enter the name of the file:
void main()
{
float **x;
int i,j;
int l,c;
char name_file[30];
FILE *res;
/* some lines omitted */
printf("\nEnter the name of the file =>");
fflush (stdin);
fgets(name_file,30,stdin);
printf("Name of file : %s", name_file);
res=creation(name_file,l,c,x);
printf("\nThe created file\n");
readfile(res,name_file);
}
The function to create the text file:
FILE *creation(char *f_name,int l, int c, float **a) // l rows - c colums - a array
{ FILE *fp;
int i,j;
fp = fopen(f_name,"wt+"); // create for writing and reading
fflush(stdin);
/* The pointer to the file is NULL: */
if (!fp)perror("fopen"); // it's returning Invalid argument
printf("%d\n",fp); //0 ??
if(fp==NULL) { printf("File could not be created!\n"); exit(1); }
fflush(stdin);
for(i=0;i<l;i++)
{
for(j=0;j<c;j++)
{
fprintf(fp,"%3.2f",a[i][j]); // enter every score of the array in the text file
}
fprintf(fp,"\n");
}
return fp;
}
Function to read the file and check if it is correct:
**void readfile(FILE *fp,char *f_name)**
{
float a;
rewind(fp);
if(fp==NULL) { printf("File %s could not open\n",f_name); exit(1); }
while(fscanf(fp,"%3.2f",&a)!= EOF)
printf("\n%3.2f",a);
fclose(fp);
}

Answer 1

There are quite a few wrong things your code.
1.
The correct signatures of main are
int main(void);
int main(int argc, char **argv)
int main(int argc, char *argv[])
See What are the valid signatures for C's main() function?
2.
The behaviour of fflush(stdin) is undefined. See Using fflush(stdin).
fflush works with output buffers, it tells the OS that is should write
the buffered content. stdin is an input buffer, flushing makes no sense.
3.
Use fgets like this:
char name_file[30];
fgets(name_file, sizeof name_file, stdin);
It's more robust using sizeof name_file because this will give you always
the correct size. If you later change the declaration of name_file to
an char array with less than 30 spaces, but forget to change the size parameter in fgets, you
might end up with a buffer overflow.
4.
You are passing to creation the uninitialized pointer p that is pointing
to nowhere. In said function you cannot read nor write with the pointer a.
You need to allocate memory prior to the call of creation. At least judging
from the code you posted.
5.
fgets preserves the newline ('\n') character, so
name_file is containing the newline character. I really don't know if newline
is allowed in file names. I did a google search but found conflicting answers.
I don't think that you want to have newlines in your file names, anyway. It's
best to remove it before passing it to fopen (which might be the reason for
the error 22):
char name_file[30];
fgets(name_file, sizeof name_file, stdin);
int len = strlen(name_file);
if(name_file[len - 1] == '\n')
name_file[len - 1] = 0;