#include<stdlib.h>
#include<stdio.h>

void display_usage(void);

int line;

int main(int argc,char*argv[])
{
    char buffer[256];
    FILE*fp;

    if(argc<2)
    {
        display_usage();
        return(1);
    }

    if ((fp=fopen(argv[1],"r"))==NULL)
    {
        fprintf(stderr,"Error opening file,%s!",argv[1]);
        return(1);
    }

    line=1;

    while(fgets(buffer,256,fp)!=NULL)
    {

        fprintf(stdout,"4d:\t%s",line++,buffer);

    }
    fclose(fp);
    return 0;

}

void display_usage(void)
{
    fprintf(stderr,"\nProper Usage is:");
    fprintf(stderr,"\n\nlist_it filename.ext\n");
}


书上说这段程序是将程序清单显示，并且显示行号，为什么我运行不出来？是何故？求解？

#include<stdlib.h>
#include<stdio.h>

void display_usage(void);

int line;

int main(int argc,char*argv[])
{
    char buffer[256];
    FILE* fp;

    if(argc<2)
    {
        display_usage();

        return(1);
    }

    if ((fp=fopen(argv[1],"r"))==NULL)
    {
        printf("Error opening file,%s!",argv[1]);
        return(1);
    }

    line=1;

    while(fgets(buffer,256,fp)!=NULL)
    {

        printf("%4d:\t%s",line++,buffer);  /*add a % before '4d'*/

    }
    fclose(fp);
    return 0;

}

void display_usage(void)
{
    printf("\nProper Usage is:");
    printf("\n\nlist_it filename.ext\n");
}

做个让你看得到的