I'm trying to print a char to a output file, however, my compilers says I'm printing an int

Question

Pass1.c: In function ‘main’:

Pass1.c:53:6: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]
 fprintf(ofp,"%s", curr); 

There's the exact error I'm getting. I'm trying to print curr to an output file using fprintf. I run the program and try to output from my input file and I end up getting s segmentation fault. I'm using c for the first time and have no idea whats going on. Here's my code:

#include <stdio.h> #include <ctype.h> void main() { int qflag, zflag, punctflag; int skip; int orgChar, decChar, codeChar; //# of original characters, decoded characters, and code sequences double perDec; FILE *ifp, *ofp; //input & output file pointers char filename[30], curr; // filename and the current character input from the file printf("Enter the filename to be scanned: "); // ask user for filename scanf("%s", filename); //user filename input ifp = fopen(filename, "r"); // open the file as read-only ofp = fopen("output.txt", "w"); // open output file as write-only while ((curr = getc(ifp)) != EOF) { // get the next char and as long as it is not the EOF, continue if (qflag && isdigit(curr)) { //qflag is true and is digit is true skip = (int) curr - 48; //skip # of digits codeChar++; //add to coded char index qflag = 0; //qflag now flase } else if (qflag) { //if q isnt followed by a interger fprintf(ofp, "q"); //print q decChar++; //added to the decoded index qflag = 0; //qflag now false } if (punctflag == 1 && isdigit(curr)) { skip = (int) curr - 48; punctflag = 0; } //If there is a special case where we have something z^g the else would be here if (zflag && ispunct(curr)) { punctflag = 1; codeChar += 2; zflag = 0; } else if (zflag) { fprintf(ofp, "z"); decChar++; zflag = 0; } //must put in the X variable!!!!!!!!!! if (curr == 'q' || curr == 'Q') { qflag = 1; } else if (curr == 'z' || curr == 'Z') { zflag = 1; } if (zflag == 0 && qflag == 0 && skip == 0) { //need x here fprintf(ofp, "%s", curr); //<------ getting issue here! decChar++; } else { skip--; } } fclose(ifp); //closes input file fclose(ofp); //closes output file }

Moreover, you actually do need curr to be an int. That is the type that getc() returns, and you need to use that type to be able to distinguish EOF from a potentially-valid character. — John Bollinger
– John Bollinger, Commented Sep 4, 2015 at 18:08

mtpc1486 · Accepted Answer · 2015-09-04 18:23:39Z

Your definition is:

char filename[30], curr;

Here filename is an array but curr is not. Here is what is correct if you want to put a string:

char filename[30], curr[size];

But you want to put a char only. In this case, don't touch to the definiton of the curr above and instead change the fprintf section as follows:

fprintf(ofp,"%c", curr);

%s is not okay because you are going to put a char, not a string.

LBes · Accepted Answer · 2015-09-04 18:08:59Z

Everything is in here

Pass1.c: In function ‘main’:

Pass1.c:53:6: warning: format ‘%s’ expects argument of type ‘char *’, but argument 3 has type ‘int’ [-Wformat=]

This is actually telling you that you used '%s' to print but you should use '%c'.

So all you have to do is change: fprintf(ofp, "%s", curr); to fprintf(ofp, "%c", curr);

Your compiler basically said it all, you simply had to read the warning. It is also just a warning so it still compiles even though it is not correct. These warnings are here to help you.

chux · Accepted Answer · 2015-09-04 18:46:21Z

Change the line

fprintf(ofp,"%s", curr);

to

fprintf(ofp,"%c", curr);

to print a single character.

Additional comments: You should use int main(void) instead of void main() and the variables perDec and decChar are not used in your program.

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