CODEWITHSUNDEEP
cprintf
lapin
lapin

Reputation: 2148

C - passing argument 1 of ‘fprintf’ makes pointer from integer without a cast

Very simple script throw this error :

passing argument 1 of ‘fprintf’ makes pointer from integer without a cast

Why is that ? The code is : 

#include <stdio.h>
#include <string.h>

int main(int argc, char *argv[])
{
FILE *FP;

if((FP = fopen("file.txt", "r+")) == NULL) {
    printf("File won't open\n");
    return(1);
}

foo(FP);

return(0);
}

int foo(FP) {

    char name[31];
    printf( "Please enter a name (within 30 char) : \n");
    gets(name);
    fprintf(FP, "%s\n", name);

    return(0);
}

Upvotes: 0

Views: 4466

Answers (4)

Aviv
Aviv

Reputation: 424

You forgot the type classifier in FP parameter in the Foo function. Surprisingly you didn´t get an warning about it. when you are compiling, please turn on the -Wall and -pedantic flag (if you are on gcc). or at least the -Wimplicit-int warning flag to avoid similar problems

Upvotes: 0

Peter - Reinstate Monica
Peter - Reinstate Monica

Reputation: 16026

The parameter FP in the declaration of foo(FP) has no type which makes it default to int. Because foo uses it as the first parameter in a call to fprintf, the int gets converted to a FILE pointer which is legal but deprecated.

Fix: Simply declare foo as int foo(FILE *FP){...}.

Edit: And yes, as LPs said, you should declare the function before use, especially if you pass or return other types than int to or from it. The declaration can either be separate from the definition, possibly in a header; or you simply move the function definition, which is also a declaration, to a place before its first use.

Upvotes: 1

M.Bakhterev
M.Bakhterev

Reputation: 93

By default the function arg in C has type int. So when you define your function the signature actually is

int foo(int FP).

You should change it to

int foo(FILE *FP)

And, of course, it would be nice to declare function before call it.

Upvotes: 1

LPs
LPs

Reputation: 16223

Change

int foo(FP) {

to 

int foo(FILE * FP) {

You must put a prototype of foo function at the top of your code.

Upvotes: 2

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