UB04⚓︎

author: Xiangzhi Liu.

Definition⚓︎

A program in a hosted environment does not define a function named main using one of the specified forms (5.1.2.2.1).

Description⚓︎

在 hosted 环境下 main 函数的定义不与如下声明兼容

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

或没有定义 main 函数

Code⚓︎

UB4.1.c

#include<stdio.h>
void main()
{
    printf("void main()\n");
}

UB4.2.c

#include<stdio.h>
double main()
{
    printf("double main()\n");
    return 1.0;
}

UB4.3.c

// comands: xxx yyy zzz
void main(double x)
{
    printf("void main(double)\nx: %llf\n",x);
}

UB4.4.c

#include<stdio.h>
// comands: xxx yyy zzz
int main(double x,char z)
{
    printf("int main(double)\nx: %lf\nz:%c\n",x,z);
    return 0;
}

Configurations⚓︎

Configuration 1.

gcc version 4.9.2

Target: x86_64-w64-mingw32

Behaviors⚓︎

Configuration 1.

UB4.1.c: Compiled and run successfully with a warning info: return type of 'main' is not 'int' [-Wmain]

Output: `void main()`

UB4.2.c: Compiled and run successfully with a warning info: return type of 'main' is not 'int' [-Wmain]

Output: `double main()`

Return value: 0

UB4.3.c: Compiled and run successfully with warning infos: + return type of 'main' is not 'int' [-Wmain] + first argument of 'main' should be 'int' [-Wmain] + 'main' takes only zero or two arguments [-Wmain]

Output:

void main(double) x: 1250137480162850900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000 UB4.4.c: Compiled and run successfully with warning infos: + first argument of 'main' should be 'int' [-Wmain] + second argument of 'main' should be 'char **' [-Wmain]

Output:

int main(double) x: 1250137480162850900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.000000 z:?

Configuration 2.

UB4.1.c: Compiled and run successfully

Output: `void main()`

UB4.2.c: Compiled and run successfully

Output: `double main()`

Return value: 14

UB4.3.c: Compiled and run successfully

Output: 
    void main(double)                                                                                    
    x: 0.000000

UB4.4.c: Compiled and run successfully

Output: 
    int main(double)
    x: 0.000000
    z:?

Advice⚓︎

定义与标准兼容的 main 函数。