1curl_printf(3) libcurl Manual curl_printf(3)
2
6 curl_maprintf, curl_mfprintf, curl_mprintf, curl_msnprintf,
7 curl_msprintf curl_mvaprintf, curl_mvfprintf, curl_mvprintf, curl_mvs‐
8 nprintf, curl_mvsprintf - formatted output conversion
9
11 #include <curl/mprintf.h>
12 int curl_mprintf(const char *format, ...);
14 int curl_mfprintf(FILE *fd, const char *format, ...);
15 int curl_msprintf(char *buffer, const char *format, ...);
16 int curl_msnprintf(char *buffer, size_t maxlength, const char *format, ...);
17 int curl_mvprintf(const char *format, va_list args);
18 int curl_mvfprintf(FILE *fd, const char *format, va_list args);
19 int curl_mvsprintf(char *buffer, const char *format, va_list args);
20 int curl_mvsnprintf(char *buffer, size_t maxlength, const char *format,
21 va_list args);
22 char *curl_maprintf(const char *format , ...);
23 char *curl_mvaprintf(const char *format, va_list args);
24
26 These functions produce output according to the format string and given
27 arguments. They are mostly clones of the well-known C-style functions
28 but there are slight differences in behavior.
29 We discourage users from using any of these functions in new applica‐
31 tions.
32 Functions in the curl_mprintf() family produce output according to a
34 format as described below. The functions curl_mprintf() and
35 curl_mvprintf() write output to stdout, the standard output stream;
36 curl_mfprintf() and curl_mvfprintf() write output to the given output
37 stream; curl_msprintf(), curl_msnprintf(), curl_mvsprintf(), and
38 curl_mvsnprintf() write to the character string buffer.
39 The functions curl_msnprintf() and curl_mvsnprintf() write at most
41 maxlength bytes (including the terminating null byte ('\0')) to buffer.
42 The functions curl_mvprintf(), curl_mvfprintf(), curl_mvsprintf(),
44 curl_mvsnprintf() are equivalent to the functions curl_mprintf(),
45 curl_mfprintf(), curl_msprintf(), curl_msnprintf(), respectively, ex‐
46 cept that they are called with a va_list instead of a variable number
47 of arguments. These functions do not call the va_end macro. Because
48 they invoke the va_arg macro, the value of ap is undefined after the
49 call.
50 The functions curl_maprintf() and curl_mvaprintf() return the output
52 string as pointer to a newly allocated memory area. The returned string
53 must be curl_free(3)ed by the receiver.
54 All of these functions write the output under the control of a format
56 string that specifies how subsequent arguments are converted for out‐
57 put.
58
61 The format string is composed of zero or more directives: ordinary
62 characters (not %), which are copied unchanged to the output stream;
63 and conversion specifications, each of which results in fetching zero
64 or more subsequent arguments. Each conversion specification is intro‐
65 duced by the character %, and ends with a conversion specifier. In be‐
66 tween there may be (in this order) zero or more flags, an optional min‐
67 imum field width, an optional precision and an optional length modi‐
68 fier.
69
72 The arguments must correspond properly with the conversion specifier.
73 By default, the arguments are used in the order given, where each '*'
74 (see Field width and Precision below) and each conversion specifier
75 asks for the next argument (and it is an error if insufficiently many
76 arguments are given). One can also specify explicitly which argument is
77 taken, at each place where an argument is required, by writing "%m$"
78 instead of '%' and "*m$" instead of '*', where the decimal integer m
79 denotes the position in the argument list of the desired argument, in‐
80 dexed starting from 1. Thus,
81 curl_mprintf("%*d", width, num);
83 and
85 curl_mprintf("%2$*1$d", width, num);
87 are equivalent. The second style allows repeated references to the same
89 argument.
90 If the style using '$' is used, it must be used throughout for all con‐
92 versions taking an argument and all width and precision arguments, but
93 it may be mixed with "%%" formats, which do not consume an argument.
94 There may be no gaps in the numbers of argu‐ ments specified using '$';
95 for example, if arguments 1 and 3 are specified, argument 2 must also
96 be specified somewhere in the format string.
97
100 The character % is followed by zero or more of the following flags:
101 # The value should be converted to its "alternate form".
103 0 The value should be zero padded.
105 - The converted value is to be left adjusted on the field bound‐
107 ary. (The default is right justification.) The converted value
108 is padded on the right with blanks, rather than on the left with
109 blanks or zeros. A '-' overrides a '0' if both are given.
110 ' ' (a space) A blank should be left before a positive number (or
112 empty string) produced by a signed conversion.
113 + A sign (+ or -) should always be placed before a number produced
115 by a signed conversion. By default, a sign is used only for neg‐
116 ative numbers. A '+' overrides a space if both are used.
117
119 An optional decimal digit string (with nonzero first digit) specifying
120 a minimum field width. If the converted value has fewer characters than
121 the field width, it will be padded with spaces on the left (or right,
122 if the left-adjustment flag has been given). Instead of a decimal digit
123 string one may write "*" or "*m$" (for some decimal integer m) to spec‐
124 ify that the field width is given in the next argument, or in the m-th
125 argument, respec‐ tively, which must be of type int. A negative field
126 width is taken as a '-' flag followed by a positive field width. In no
127 case does a nonexistent or small field width cause truncation of a
128 field; if the result of a conversion is wider than the field width, the
129 field is expanded to contain the conversion result.
130
132 An optional precision in the form of a period ('.') followed by an op‐
133 tional decimal digit string. Instead of a decimal digit string one may
134 write "*" or "*m$" (for some decimal integer m) to specify that the
135 precision is given in the next argument, or in the m-th argument, re‐
136 spectively, which must be of type int. If the precision is given as
137 just '.', the precision is taken to be zero. A negative precision is
138 taken as if the precision were omitted. This gives the minimum number
139 of digits to appear for d, i, o, u, x, and X conversions, the number of
140 digits to appear after the radix character for a, A, e, E, f, and F
141 conversions, the maximum number of significant digits for g and G con‐
142 versions, or the maximum number of characters to be printed from a
143 string for s and S conversions.
144
146 h A following integer conversion corresponds to a short or un‐
147 signed short argument.
148 l (ell) A following integer conversion corresponds to a long or
150 unsigned long argument, or a following n conversion corresponds
151 to a pointer to a long argument
152 ll (ell-ell). A following integer conversion corresponds to a long
154 long or unsigned long long argument, or a following n conversion
155 corresponds to a pointer to a long long argument.
156 q A synonym for ll.
158 L A following a, A, e, E, f, F, g, or G conversion corresponds to
160 a long double argument.
161 z A following integer conversion corresponds to a size_t or
163 ssize_t argument.
164
166 A character that specifies the type of conversion to be applied. The
167 conversion specifiers and their meanings are:
168 d, i The int argument is converted to signed decimal notation. The
170 precision, if any, gives the minimum number of digits that must
171 appear; if the converted value requires fewer digits, it is
172 padded on the left with zeros. The default precision is 1. When
173 0 is printed with an explicit precision 0, the output is empty.
174 o, u, x, X
176 The unsigned int argument is converted to unsigned octal (o),
177 unsigned decimal (u), or unsigned hexadecimal (x and X) nota‐
178 tion. The letters abcdef are used for x conversions; the letters
179 ABCDEF are used for X conversions. The precision, if any, gives
180 the minimum number of digits that must appear; if the converted
181 value requires fewer digits, it is padded on the left with ze‐
182 ros. The default precision is 1. When 0 is printed with an ex‐
183 plicit precision 0, the output is empty.
184 e, E The double argument is rounded and output in the style
186 "[-]d.ddde±dd"
187 f, F The double argument is rounded and output to decimal notiation
189 in the style [-]ddd.ddd.
190 g, G The double argument is converted in style f or e.
192 c The int argument is converted to an unsigned char, and the re‐
194 sulting character is written.
195 s The const char * argument is expected to be a pointer to an ar‐
197 ray of character type (pointer to a string). Characters from the
198 array are written up to (but not including) a terminating null
199 byte. If a precision is specified, no more than the number spec‐
200 ified are written. If a precision is given, no null byte need be
201 present; if the precision is not specified, or is greater than
202 the size of the array, the array must contain a terminating null
203 byte.
204 p The void * pointer argument is printed in hexadecimal.
206 n The number of characters written so far is stored into the inte‐
208 ger pointed to by the corresponding argument.
209 % A '%' is written. No argument is converted.
211
213 mprintf("My name is %s\n", name);
214 mprintf("Pi is almost %f\n", 25/8);
215
217 These functions will be removed from the public libcurl API in the fu‐
218 ture. Do not use them in new programs or projects.
219
221 The curl_maprintf and curl_mvaprintf functions return a pointer to a
222 newly allocated string, or NULL if it failed.
223 All other functions return the number of characters actually printed
225 (excluding the null byte used to end output to strings). Note that this
226 sometimes differ from how the POSIX versions of these functions work.
227
229 printf(3), sprintf(3), fprintf(3), vprintf(3)
230libcurl 7.82.0 November 26, 2021 curl_printf(3)