程序代码：

#include <stdlib.h>
#include <string.h>

int compare( const void* a, const void* b )
{
    return strcmp( *(const char**)a, *(const char**)b );
}

int main()
{
    const char* str = "abcdewoiabwewog";

    //////////////////////

    const size_t len = strlen( str );
    const char* ps[len];
    for( size_t i=0; i!=len; ++i )
        ps[i] = str+i;
    qsort( ps, len, sizeof(ps[0]), &compare );

    size_t maxlen = 0;
    size_t maxidx = 0;
    for( size_t i=0; i!=len-1; ++i )
    {
        const char* a = ps[i];
        const char* b = ps[i+1];

        size_t idlen = 0;
        for( ; a[idlen]!='\0' && a[idlen]==b[idlen]; ++idlen );

        if( idlen > maxlen )
        {
            maxlen = idlen;
            maxidx = (a-str)<=(b-str) ? (a-str) : (b-str);
        }
    }

    printf( "start: %d; length: %d; value: %.*s\n", maxidx, maxlen, maxlen, str+maxidx );

    return 0;
}

程序代码：

#include <stdlib.h>
#include <string.h>

int main()
{
    const char* str = "abcdewoiabwewog";
    int f[100][100]={0},maxlen=0,len=strlen(str),start,i,j,k;
    
    for (i=1; i<len; i++) if (str[0]==str[i]) f[0][i]=1;
    for (i=1; i<len; i++)
        for (j=i+1; j<len; j++)
        {   
            if (str[i]==str[j]) f[i][j]=f[i-1][j-1]+1; 
                           else f[i][j]=0;
            if (f[i][j]>maxlen)
            {
                               maxlen=f[i][j];
                               start=i-maxlen+1;
            }
        }
    printf("Maxlen=%d Start=%d End=%d\n",maxlen,start,start+maxlen-1);
    
    system("pause");
    return 0;
}