Xcode-Police: 函数的隐式声明在 C99中无效

获取警告: 在 C99中，函数“ Fibonacci”的隐式声明无效。 怎么了？

#include <stdio.h>


int main(int argc, const char * argv[])
{
int input;
printf("Please give me a number : ");
scanf("%d", &input);
getchar();
printf("The fibonacci number of %d is : %d", input, Fibonacci(input)); //!!!


}/* main */


int Fibonacci(int number)
{
if(number<=1){
return number;
}else{
int F = 0;
int VV = 0;
int V = 1;
for (int I=2; I<=getal; I++) {
F = VV+V;
VV = V;
V = F;
}
return F;
}
}/*Fibonacci*/
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The compiler wants to know the function before it can use it

just declare the function before you call it

#include <stdio.h>


int Fibonacci(int number); //now the compiler knows, what the signature looks like. this is all it needs for now


int main(int argc, const char * argv[])
{
int input;
printf("Please give me a number : ");
scanf("%d", &input);
getchar();
printf("The fibonacci number of %d is : %d", input, Fibonacci(input)); //!!!


}/* main */


int Fibonacci(int number)
{
//…
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最佳答案

The function has to be declared before it's getting called. This could be done in various ways:

  • Write down the prototype in a header
    Use this if the function shall be callable from several source files. Just write your prototype
    int Fibonacci(int number);
    down in a .h file (e.g. myfunctions.h) and then #include "myfunctions.h" in the C code.

  • Move the function before it's getting called the first time
    This means, write down the function
    int Fibonacci(int number){..}
    before your main() function

  • Explicitly declare the function before it's getting called the first time
    This is the combination of the above flavors: type the prototype of the function in the C file before your main() function

As an additional note: if the function int Fibonacci(int number) shall only be used in the file where it's implemented, it shall be declared static, so that it's only visible in that translation unit.

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I have the same warning (it's make my app cannot build). When I add C function in Objective-C's .m file, But forgot to declared it at .h file.

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in c The function has to be declared before it's getting called

include head file


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