#1
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How to use strcat in c?
Hi,
Today I decided to code a small program that could make a backup file. I wanted to change the extension of the given file to "BAK" to be able to make a backup file. So I coded the below program but when I tried to use strcat(); function to change the extension of the given file to a backup file I faced a problem and I was not able to handle it. Finally after pondering a lot,I changed my program and used a for loop to be able to solve the problem. You can see this loop in the second program which is below. But it was not what i wanted to do. I wanted to use strcat(); function and I hope someone can help me to correct the first program. Thanks in advance. Best Regards, Zest. The imcomplete program: Code:
#include <stdio.h> #include <conio.h> #include <stdlib.h> #include <string.h> #define SIZE 40 int main(int argc,char * argv[]) { FILE *in,*out; char name[SIZE],chr = '.',bk[] = "Bak",ch; char *occurance; if(argc != 2) { puts("This program makes a BackUp of your files"); fprintf(stderr,"Usage: %s filename\n",argv[0]); exit(EXIT_FAILURE); } if((in = fopen(argv[1],"r")) == NULL) { fprintf(stderr,"I can't open the file %s",argv[1]); exit(EXIT_FAILURE); } strncpy(name,argv[1],SIZE-5); name[SIZE-5] = '\0'; occurance = strchr(name,chr); strcat(occurance , bk); if((out = fopen(name, "w")) == NULL) { fprintf(stderr,"I can't copy to the file %s",name); exit(EXIT_FAILURE); } //Copying Data while((ch = getc(in))!= EOF) putc(ch,out); if(fclose(in) != 0 || fclose(out) != 0) fprintf(stderr,"Error is closing files.\n"); puts("Done!\n"); getch(); return 0; } Code:
#include <stdio.h> #include <conio.h> #include <stdlib.h> #include <string.h> #define SIZE 40 int main(int argc, char* argv[]) { FILE *in,*out; char name[SIZE],chr = '.',bk[] = ".Bak",ch; char *occurance; if(argc != 2) { puts("This program makes a BackUp of your files"); fprintf(stderr,"Usage: %s filename\n",argv[0]); exit(EXIT_FAILURE); } if((in = fopen(argv[1],"r")) == NULL) { fprintf(stderr,"I can't open the file %s",argv[1]); exit(EXIT_FAILURE); } strncpy(name,argv[1],SIZE-5); name[SIZE-5] = '\0'; occurance = strchr(name,chr); for(int i = 0; i < 4; i++) *(occurance + i) = bk[i]; if((out = fopen(name, "w")) == NULL) { fprintf(stderr,"I can't copy to the file %s",name); exit(EXIT_FAILURE); } //Copying Data while((ch = getc(in))!= EOF) putc(ch,out); if(fclose(in) != 0 || fclose(out) != 0) fprintf(stderr,"Error is closing files.\n"); puts("Done!\n"); getch(); return 0; } |
#2
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Now why would you want to use strcat?? This routine you have now is quite slow reading on a character base is too slow. Use fread and fwrite.
strcat useage is as follows: ... char dest[20]; dest[0]='\'; strcat(dest,"this is a "); //now dest="this is a\0" strcat(dest,"test"); //now dest="this is a test\0" strcat(dest,"123456789012345678901234567890"); //now you get a crash because your dest string overflows, so this is a buffer overflow. Easier loop: char buffer[1024]; ... while !feof(in){ nrbytes=fread(buffer,1,1024,in); if (nrbytes) fwrite(buffer,1,nrbytes,out); } etc.. Backupping files can be done faster using windows functions if yer running windoze. |
#3
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Just some small remarks regarding your program.
It seems that it can not handle well an extension of 1 or 2 characters or more than 3 characters. You should start from the back of the file name (argv[1]) and search for the last point '.' character. And BTW, you don't need to use strcat in case you have at least 3 characters for extension. Just find the last '.' in the name and replace the next 4 characters with "BAK" and '\0'. The other remarks from piccolo also remain. |
#4
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Don't know if it's useful for you, but you could use the API PathRenameExtension , which is in shlwapi.dll, this API replace any extension with any extension you want:
PathRenameExtension ("file.ext", ".bak"); Hope it works for you, just #include <shlwapi.h> This only works in windows, off course... |
#5
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Here is a generalized routine good for your situation
and can be easily tailored or adapted to fit most any situation: // EX: OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE. // Find the last '\\' to obtain a pointer to just the base file name part if your buffer contains any path type info // We could just as eaily searched for last '.' to obtain base file name extension pointer. Code:
char *szBuffer = buffer; PCSTR pszBaseName = strrchr( szBuffer, '\\' ); if ( pszBaseName ) // We found a '\\', so advance to the base FILE name { // Increment 1 byte past our pointer pszBaseName++; strncpy(pszBaseName, "Asprlog.txt\0", 12); // we need 12 to include '\0' null char //replace base file name with newname , here you could have appended bak or BAK extension if you had searched on the '.' char Ex: as so: strncpy(pszBaseName, "bak\0", 4); } FILE * pFile; pFile=fopen(szBuffer,"wt"); // open for write cheers! |
#6
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maybe you could try the following routine to search for the '.' from the end of the filename:
Code:
char Filename[]= "c:\\path\\file.ext"; char *BaseFileName; strrev(Filename); BaseFileName = strstr(Filename,"."); // search for the '.' if (BaseFileName){ BaseFileName = (char*)(BaseFileName+1); // exclude the '.' strcpy(Filename,BaseFileName); } strrev(Filename); strcat(Filename,".bak\0"); well of course there are still a bunch of ways to implement this. anyways, hope this helps... |
#7
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Quote:
fnsplit() , fnmerge() i think its in dir.h splitpath() , makepath() defined in stdlib.h these all take care to find . on thier own all you need to give is buffers for specific paths and then just switch what you dont with what you need and compose back |
#8
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Dear condzero,
Hi, Thanks for your help and reply. But there is still a problem for me that I couldn't manage it. Would you please let me know how to OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE? Which function(s) do you use to OPEN A FILE FOR LOGGING OUTPUT IN ANALYZE MODE? That would be great if you can discuss the case a bit. I look forward to hearing from you. Also thank anybody else who has spend time to answer to this topic to bring some help to the point. Regards, Zest. |
#9
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Hi Zest,
Not sure what you mean by "Analyze Mode". In my example, I open a file with the parameter "wt" (Write, text mode). Then I simply create my output: Code:
char b[1024]; unsigned int o = 0; //Loop counter FILE * pFile; pFile=fopen("myfile.txt","wt"); // open for write text mode // Use a loop and print your output, or just keep appending data to a buffer then print the entire buffer (Note: Use of new line char n) LOOP: sprintf( b, "Some text\n") fputs (b,pFile); // or possibly fwrite (b , 1 , 80 , pFile); (where 80 is the length of your text, not sure which way is more applicable as I generally use the code below) ... //or for ( o = 0; o < strlen(b); o++ ) { putc(b[o], pFile); } // CLOSE THE FILE. fclose (pFile); Perhaps others can elaborate more. cheers. |
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