C文件操作 —— 在文件中查找关键字并替换

2011-03-30 wcdj

问题描述：
有一个txt文件，里面的数据是这个样子
980000001 AAE134D000
980000002 0AF2EBCE00
......
980000098 0ABDCEDB2A
......

现在有一个新数据
980000098 5ACBDC5BDC
想替换原来的那一行数据

 

原问题：http://topic.csdn.net/u/20110330/16/6e4f6070-d3c6-4a2f-8394-04e3a8cb9a7e.html

方法1：如果每一行记录的长度是一样的，则可以通过fseek直接在原文件中修改。
#include <cstdio>#include <cstdlib>#include <cstring>int main(){FILE *in = NULL;if( (in = fopen("test.txt","rt+")) == NULL )// Note "rt+"return -1;int get1, find;char str[16]="";printf("Please enter number to replace: ");while (rewind(stdin), scanf("%d %s", &find, str) != 2)printf("Please input again: ");char tmp[128] = "";while (fscanf(in,"%d %*s", &get1) != EOF){if (get1 == find){int res = fseek(in, -20L, SEEK_CUR);// sizeof(980000001 AAE134D000) == 20Bitoa(find, tmp, 10);strcat(tmp, " ");strcat(tmp, str);// replace your stringstrcat(tmp, "/n");fputs(tmp, in);break;}}fclose(in);return 0;}/*980000001 AAE134D000980000002 0AF2EBCE00980000098 0ABDCEDB2A*/

 

修改一下代码，如果每行固定最长为20，下面代码允许后面的字符串长度小于10，但不能大于10，否则会覆盖下面的合法数据。实现的原理是，如果字符串小于10，将后面多余的字符串用空格字符串覆盖。( 测试过程中，发现下面代码仍有问题 )
#include <cstdio>#include <cstdlib>#include <cstring>int main(){FILE *in = NULL;if( (in = fopen("test.txt","rt+")) == NULL )// Note "rt+"return -1;int get1, find;char str[16]="";printf("Please enter number to replace: ");while (rewind(stdin), scanf("%d %s", &find, str) != 2)printf("Please input again: ");char tmp[128] = "";int beg = 0, end = 0;int line = 0;bool bfirst = true;int nwrite = 0, nleft;beg = end = ftell(in);while (fscanf(in,"%d %*s", &get1) != EOF){bfirst ? NULL, bfirst=false : line+=2;// because of "/r/n" beg = end;end = ftell(in);if (get1 == find){int res1 = fseek(in, -(end-beg-line), SEEK_CUR);int t1 = ftell(in);itoa(find, tmp, 10);strcat(tmp, " ");strcat(tmp, str);// replace your stringfputs(tmp, in);int t2 = ftell(in);// clear useless charactersnwrite = strlen(tmp);if (nwrite < 20){nleft = 20 -nwrite;memset(tmp, ' ', nleft);tmp[nleft]='/0';fputs(tmp, in);}break;}}fclose(in);return 0;}/*980000001 AAE134D000980000002 0AF2EBCE00980000098 0ABDCEDB2A*/

 

方法2：如果每一行记录的长度不同，只能输出到另外一个文件。

#include <cstdio>#include <cstdlib>#include <cstring>int main(){FILE *in = NULL, *out = NULL;if( (in = fopen("test.txt","r+")) == NULL )return -1;if( (out = fopen("test2.txt","a")) == NULL )return -1;int get1, find;char str[16]="";printf("Please enter number to replace: ");while (rewind(stdin), scanf("%d %s", &find, str) != 2)printf("Please input again: ");char get2[16] = "", tmp[128] = "";while (fscanf(in,"%d %s", &get1, &get2) != EOF){if (get1 == find){itoa(find, tmp, 10);strcat(tmp, " ");strcat(tmp, str);// replace ur stringstrcat(tmp, "/n");fputs(tmp, out);}else{itoa(get1, tmp, 10);strcat(tmp, " ");strcat(tmp, get2);strcat(tmp, "/n");fputs(tmp, out);}}fclose(in);fclose(out);return 0;}/*980000001 AAE134D000980000002 0AF2EBCE00980000098 0ABDCEDB2A*/

 

参考：
fopen
http://www.cplusplus.com/reference/clibrary/cstdio/fopen/
fseek
http://www.cplusplus.com/reference/clibrary/cstdio/fseek/
fputs
http://www.cplusplus.com/reference/clibrary/cstdio/fputs/
ftell
http://www.cplusplus.com/reference/clibrary/cstdio/ftell/