base64 c语言源码

/* base64.c: MIME BASE64编码与解码器,读标准输入. 赵建军, 2000.1.12.a */ /* 2000.2.19.A: 增文件处理. */ #include "stdio.h" #include "string.h" #include "stdlib.h" #include "ctype.h" char *base="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; union { struct { unsigned long d:6; unsigned long c:6; unsigned long b:6; unsigned long a:6; }s; unsigned char c[3]; }u; int decode=0; main(int argc,char **argv) { extern char *optarg; extern int optind; int c; FILE *fp; while ((c=getopt(argc,argv,"u"))!=EOF) { switch(c) { case 'u': decode=1; break; default: usage(); break; } } if (argc==optind) { if (isatty(0)) usage(); if (decode) base64decode(stdin,stdout); else base64encode(stdin,stdout); } else for (;optind<argc;optind++) { fp=fopen(argv[optind],"r"); if (fp==0) { fprintf(stderr,"%s: fopen %s error.\n",argv[0],argv[optind]); continue; } if (decode) base64decode(fp,stdout); else base64encode(fp,stdout); fclose(fp); } exit(0); } usage() { fprintf(stderr,"base64: MIME BASE64 encoder and decoder, by zzz ([email protected]) at 2000.1.11.m\n"); fprintf(stderr,"Usage: base64 [-u] [file1] [file2] ...\n"); exit(1); } base64encode(FILE *fp,FILE *fq) { int ch,n,h=0,flag=0; while (1) { u.c[0]=u.c[1]=u.c[2]=0; for (n=0;n<3;n++) { ch=fgetc(fp); if (ch==EOF) break; u.c[2-n]=ch; } if (n==0) break; flag=1; switch(n) { case 1: fprintf(fq,"%c%c==",base[u.s.a],base[u.s.b]);break; case 2: fprintf(fq,"%c%c%c=",base[u.s.a],base[u.s.b],base[u.s.c]);break; case 3: fprintf(fq,"%c%c%c%c",base[u.s.a],base[u.s.b],base[u.s.c],base[u.s.d]);break; } if (h==15) { h=0; fprintf(fq,"\n"); } else h++; } if (flag&&h) fprintf(fq,"\n"); } base64decode(FILE *fp,FILE *fq) { int c1,c2,c3,c4; while (1) { /* c1 */ c1=fgetc(fp); while (c1!=EOF&&isspace(c1)) c1=fgetc(fp); if (c1==EOF) break; if (strchr(base,c1)==NULL&&c1!='=') { fprintf(fq,"Error: %c : not BASE64 code!\n",c1); return 1; } /* c2 */ c2=fgetc(fp); if (c2==EOF) { fprintf(fq,"Error: unexpected EOF in BASE64 code!\n"); return 1; } if (strchr(base,c2)==NULL&&c2!='=') { fprintf(fq,"Error: %c : not BASE64 code!\n",c2); return 1; } /* c3 */ c3=fgetc(fp); if (c3==EOF) { fprintf(fq,"Error: unexpected EOF in BASE64 code!\n"); return 1; } if (strchr(base,c3)==NULL&&c3!='=') { fprintf(fq,"Error: %c : not BASE64 code!\n",c3); return 1; } /* c4 */ c4=fgetc(fp); if (c4==EOF) { fprintf(fq,"Error: unexpected EOF in BASE64 code!\n"); return 1; } if (strchr(base,c4)==NULL&&c4!='=') { fprintf(fq,"Error: %c : not BASE64 code!\n",c4); return 1; } /* check format:[A-Za-z0-9+/][A-Za-z0-9+/][A-Za-z0-9+/=][A-Za-z0-9+/=] */ if (strchr(base,c1)&&strchr(base,c2)&&(strchr(base,c3)||c3=='=')&& ((c3=='='&&c4=='=')||(c3!='='&&(c4=='='||strchr(base,c4))))) { u.s.a=strchr(base,c1)-base; u.s.b=strchr(base,c2)-base; if (c3=='=') { /* one byte output */ fprintf(fq,"%c",u.c[2]); } else if (c4=='=') { /* two byte output */ u.s.c=strchr(base,c3)-base; fprintf(fq,"%c%c",u.c[2],u.c[1]); } else { /* three byte output */ u.s.c=strchr(base,c3)-base; u.s.d=strchr(base,c4)-base; fprintf(fq,"%c%c%c",u.c[2],u.c[1],u.c[0]); } } else { fprintf(fq,"Error: %c%c%c%c : not BASE64 code!\n",c1,c2,c3,c4); return 1; } } return 0; }