Linux c基础学习

<br>#include <stdio.h>

#include <stdlib.h>

int myarray[50000]={1,2,3,4,5};

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

{

    return 0;

}

#include <stdio.h>

#include <stdlib.h>

int myarray[50000];

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

{

    myarray[0]=3;

    return 0;

}

#include <stdio.h>

#include <stdlib.h>

extern char ** environ;

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

{

    int i;

    printf("The environment list is as floows:\n");

    for ( i = 0; environ[i]!=NULL; ++i)

        {

            printf("*environ[%d]: %s\n",i,environ[i] );

        }  

    return 0;

}

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#include <stdio.h>

#include <stdlib.h>

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

{

    char* str;

    str=getenv("PATH");

    if(str!=NULL){

        printf("%s\n",str );

    }else{

        printf("doesn't exits PATH \n");

    }

    return 0;

}

#include <stdio.h>

#include <stdlib.h>

#include <limits.h>

#include <unistd.h>

#include <sys/times.h>

static void showtimes()

{

    double ticks;

    struct tms tinfo;

    if((ticks=(double)sysconf(_SC_CLK_TCK))== -1){

        perror("Filed to detemine clock ticks per second\n");

    }else if(times(&tinfo)==(clock_t)-1){

        perror("Filed to get times infomation\n");

    }else{

        fprintf(stderr, "user time:  %f seconds\n",tinfo.tms_utime/ticks );

        fprintf(stderr, "system time:  %f seconds\n",tinfo.tms_stime/ticks );

        fprintf(stderr, "childermn's user time:  %f seconds\n",tinfo.tms_cutime/ticks );

        fprintf(stderr, "childermn's system time:  %f seconds\n",tinfo.tms_cstime/ticks );

    }

}

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

{

    if(atexit(showtimes)){

        fprintf(stderr, "Filed to install showtimes function\n" );

        exit(1);

    }

    return 0;

}

#include <stdio.h>

#include <stdlib.h>

static void function1();

static void function2();

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

{

    printf("main function start...\n");

    if(atexit(function1)){

        fprintf(stderr, "atexit function calls error\n");

        exit(1);

    }

    if (atexit(function2))

    {

        fprintf(stderr, "atexit function calls error\n");

        exit(1);

    }

    printf("main function end...\n");

    return 0;

}

static void function1(){

    printf("This is function1\n");

}

static void function2(){

    printf("This is function2\n");

}

/*

    this program run result as follows:

    main function start...

    main function end...

    This is function2

    This is function1

*/

#include <stdlib.h>

#include <stdio.h>

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

{

    system("ps ax");

    return 0;

}